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Discussion Starter · #1 · (Edited)
With Coharie Bolt - .017" (.43mm)

With HK Bolt - .027 (.70mm)


Why would the hk Bolt be so high? -4 rollers would bring it down, but would there be any other problems since the original gap was so high?

The hk bolt is brand new. Just curious to see what factors could contribute to the difference in gap.
 

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If the slot for the rollers is closer to the rear of the bolt head on the CA bolt than the HK bolt, the gap will be larger.

What sucks is that if you correct the gap with different sized rollers, you may actually be making the problem worse, or causing a problem that wasn't there before.

Here's what I mean by that. Forget for the moment that you have a CA bolt. Let's assume that you had an HK bolt head all along, and the gap was an almost perfect .016" with +4 rollers. Now take that bolt out and grind .020" off the back of it. Your gap will now be .036", which appears to be way out of spec. But you haven't change one single thing on the end that counts. The relationship between the bolt face, rollers, trunnion, and locking piece haven't changed at all. So if you now install -4 rollers to get the gap back down to "in spec" you'll end up with a trunnion/bolt head/roller relationship as if you had the original rollers and a zero bolt gap.

Thinking out loud - I wonder if you could make accurate measurements of the roller slot in the two bolt heads to see if that's where the difference is? I might try something like that. If they are different, then you might need to use a different 'acceptable range' for your bolt gap.

The tricky part is that a bolt gap is a measurement to determine the relationship between the bolt head and the trunnion at the front of a mechanical system, but the measurement it taken at the back end of that system.

Know what I mean, Verne?
 

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and if the parts are in spec to start with..

if using Hk Clone Parts..who know's what it would be...
using Hk and FMP parts. bolt heads. i have seen a a diff of +2 with tha same rollers. just swaping bolt heads..
i have never seen more then +2 in gap with bolt heads.
with parts that are in spec..per Hk & FMP.
PARTS AND GUN'S (not clones)

the gun is only as good. as the parts used.

stick with good known parts that take a beating..
 

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If the slot for the rollers is closer to the rear of the bolt head on the CA bolt than the HK bolt, the gap will be larger.

What sucks is that if you correct the gap with different sized rollers, you may actually be making the problem worse, or causing a problem that wasn't there before.

Here's what I mean by that. Forget for the moment that you have a CA bolt. Let's assume that you had an HK bolt head all along, and the gap was an almost perfect .016" with +4 rollers. Now take that bolt out and grind .020" off the back of it. Your gap will now be .036", which appears to be way out of spec. But you haven't change one single thing on the end that counts. The relationship between the bolt face, rollers, trunnion, and locking piece haven't changed at all. So if you now install -4 rollers to get the gap back down to "in spec" you'll end up with a trunnion/bolt head/roller relationship as if you had the original rollers and a zero bolt gap.

Thinking out loud - I wonder if you could make accurate measurements of the roller slot in the two bolt heads to see if that's where the difference is? I might try something like that. If they are different, then you might need to use a different 'acceptable range' for your bolt gap.

The tricky part is that a bolt gap is a measurement to determine the relationship between the bolt head and the trunnion at the front of a mechanical system, but the measurement it taken at the back end of that system.

Know what I mean, Verne?
what you are alluding to, is the fact that the Coharie bolt and the HK bolt might be different lengths.

That dimension is easily checked with calipers.

However, if they are the same length, and the bolt gap is different (which might be the case) the difference in bolt gap illustrates how deep the rollers are seating in the trunnion, thus showing that his gun will now unlock much too easily.

Tabasco- do you have calipers? take some measurements of both bolts... just for fun.

Oh, also- your locking piece is of course be playing a role as well.

But also... if the bolts have roller slots in different places, that would of course change the system.

I continue to be amazed that bolts can not be built to the proper dimensions. I mean, whiskey tango foxtrot?
 

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what you are alluding to, is the fact that the Coharie bolt and the HK bolt might be different lengths.

That dimension is easily checked with calipers.

However, if they are the same length, and the bolt gap is different (which might be the case) the difference in bolt gap illustrates how deep the rollers are seating in the trunnion, thus showing that his gun will now unlock much too easily.

Tabasco- do you have calipers? take some measurements of both bolts... just for fun.

Oh, also- your locking piece is of course be playing a role as well.

But also... if the bolts have roller slots in different places, that would of course change the system.

I continue to be amazed that bolts can not be built to the proper dimensions. I mean, whiskey tango foxtrot?
The length of the bolt head is just one measurement to check. There are actually 2 measurements that are critical if you want to use the HK bolt gap range on a Coharie bolt head -

1. Overall length
2. Distance between front of bolt head and front wall of slot

Both of those must be the same as the ones on an HK bolt gap for the HK spec to apply. The reason being is that even if the two bolts are the exact same length, but the front wall of the roller slot is closer or further from the bolt head face, the gap will change.

He hasn't changed the locking piece, so it is irrelevant. But since nobody knows what the proper range should be with his CA parts (not even CA I suspect since their parts are supposed to be interchangeable but aren't), even with the measurements there's know way of knowing what they should be.

Is .017" correct for CA parts? No idea. It is for all HK parts, but with a mix of HK and CA parts, there's no way to know besides just using it and seeing how it works.
 

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The length of the bolt head is just one measurement to check. There are actually 2 measurements that are critical if you want to use the HK bolt gap range on a Coharie bolt head -

1. Overall length
2. Distance between front of bolt head and front wall of slot

Both of those must be the same as the ones on an HK bolt gap for the HK spec to apply. The reason being is that even if the two bolts are the exact same length, but the front wall of the roller slot is closer or further from the bolt head face, the gap will change.

He hasn't changed the locking piece, so it is irrelevant. But since nobody knows what the proper range should be with his CA parts (not even CA I suspect since their parts are supposed to be interchangeable but aren't), even with the measurements there's know way of knowing what they should be.

Is .017" correct for CA parts? No idea. It is for all HK parts, but with a mix of HK and CA parts, there's no way to know besides just using it and seeing how it works.
yeah, like I said, if the slots are in the wrong spot, all bets are off too.

As far as what Coharie thinks, Todd has said on multiple occasions that the guns like 0.020", or thereabouts, the best. (could be because of rifle spring though too). The more resistance in the system, the bigger you want the bolt gap, because you want the gun to be able to unlock.

The HK design is an engineering thing of beauty. But, all the parts have to work together. If there are some bad apples in the bunch, the whole thing is off.

The reason I talked about the locking piece, is because the locking piece from Coharie could be fine for the incorrectly dimensioned Coharie bolt, but when put in an HK bolt, it may be slightly too wide or something (which would make the bolt gap bigger, because it would push the rollers out more).

He hasn't changed the locking piece, but I bet that if he DID change it (to a proper HK locking piece) the bolt gap would change again.

Every piece in the action of that rifle has to be to the correct dimensions...

If you have a correctly dimensioned bolt head, locking piece, and rollers, and your bolt gap is still off..... either the carrier is really messed up some how, or the trunnion is messed up, or the barrel is not pressed correctly.

How's that for a list of possible problems? lol
 

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I continue to be amazed that bolts can not be built to the proper dimensions. I mean, whiskey tango foxtrot?
I continue to be amazed by the people that have to insist on buying and installing genuine HK parts when there's nothing wrong with the gun in the first place.

I mean, what's wrong with a .017 bolt gap??
 

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I continue to be amazed by the people that have to insist on buying and installing genuine HK parts when there's nothing wrong with the gun in the first place.

I mean, what's wrong with a .017 bolt gap??
don't just insinuate that people just buy HK bolts to fix bolt gap.

My Coharie bolt (of which I have had 2) both are OUT OF SPEC.

The first bolt would not accept an HK extractor, and the round wouldn't sit against the bolt face properly.

The second bolt DOES fit an HK extractor, but does so loosely, that the extractor (ANY extractor) wiggles and shifts, even when using BRAND NEW copper OR silver extractor springs. This causes problems as well.

What is the solution to this? A new bolt head.

Or, I could call Coharie, and get a 3rd bolt head. How about NO F'ING WAY. Not worth my time.

I bought an HK bolt head, because I KNOW it will work.

I'm not sure why Tabasco bought one. I'm assuming it is for reasons similar to mine.
 

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Every piece in the action of that rifle has to be to the correct dimensions...

If you have a correctly dimensioned bolt head, locking piece, and rollers, and your bolt gap is still off..... either the carrier is really messed up some how, or the trunnion is messed up, or the barrel is not pressed correctly.

How's that for a list of possible problems? lol
Now you're getting to my point - blindly replacing CA parts with HK parts may cause problems that aren't there. A given combination of CA trunion, locking piece, rollers, bolt head, and carrier may provide the correct geometry up at the breech face, but the gap may or may not be within HK's range.

If you just randomly start replacing CA parts with HK parts, sure, you may get the bolt gap back at HK spec, but it may screw up the geometry up at the breech face, or at the roller/trunion junction, which is where it really matters.

For all we know, CA might be matching oversized locking pieces with undersized rollers, or custom cutting this part or that part to fit the rest of the parts (like the ones they grind on). Without calipers or mics, randomly replacing parts is just shooting in the dark.

Anybody have any CA parts you're not using any more? I'd love to borrow some and measure to see where they are different. Maybe we could find some patterns and know what to tell people to check and what to change. One problem may be that they have been made by several different suppliers, so there may be several different dimensions of the parts.
 

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Now you're getting to my point - blindly replacing CA parts with HK parts may cause problems that aren't there. A given combination of CA trunion, locking piece, rollers, bolt head, and carrier may provide the correct geometry up at the breech face, but the gap may or may not be within HK's range.

If you just randomly start replacing CA parts with HK parts, sure, you may get the bolt gap back at HK spec, but it may screw up the geometry up at the breech face, or at the roller/trunion junction, which is where it really matters.

For all we know, CA might be matching oversized locking pieces with undersized rollers, or custom cutting this part or that part to fit the rest of the parts (like the ones they grind on). Without calipers or mics, randomly replacing parts is just shooting in the dark.

Anybody have any CA parts you're not using any more? I'd love to borrow some and measure to see where they are different. Maybe we could find some patterns and know what to tell people to check and what to change. One problem may be that they have been made by several different suppliers, so there may be several different dimensions of the parts.
I agree completely.

The problem occurs when you HAVE to replace a part. See, if you have to replace your bolt head because extractors don't seat in it correctly, you are then gambling that the tolerances and dimensions of the existing locking piece and rollers will be such that everything will be fine when you replace the bolt.

But, it looks like that in this case, everything was not fine. He's probably going to have to see if a new locking piece lowers the gap, or maybe just use smaller rollers.

Either way, you change one component in that group- it's all shot to hell- and that's not how it would be if it was HK parts. The only reason it's like that, is because every freakin part in that gun is off by some small amount- and the small amount is enough to mess everything up.

Of all the things to clone..... a roller-locked delayed blow-back rifle is probably one of the most difficult. The precise timing of the system, the exact geometries, everything that is needed to make it work correctly.... it is AMAZING they work the way they do. Any little mistake... and you pay for it. Not a forgiving design, in the least.
 

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The second bolt DOES fit an HK extractor, but does so loosely, that the extractor (ANY extractor) wiggles and shifts, even when using BRAND NEW copper OR silver extractor springs. This causes problems as well.
That's why I replaced my CA bolt. HK Bolt & RIM locking piece with standard rollers equaled the CA w/+2 rollers.
 

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That's why I replaced my CA bolt. HK Bolt & RIM locking piece with standard rollers equaled the CA w/+2 rollers.
Yup, I remember you saying that.

Luckily, those parts (rollers/locking piece) are relatively cheap- so I hope this guy can get his stuff dialed-in. I'm thinking he can.
 

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Discussion Starter · #14 · (Edited)
No luck on calipers, my brother from Austin is coming to town next week I'll see then.


The CA bolt with g3 extractor spring works 100%. 235 rounds so far and every single round ejected strong. I bought the HK Bolt b/c it was only $250 shipped (new) and I assume it would be harder to get since HK is blocking sales. Also its nice to have a spare part.

Just tried my POF locking piece again, the bolt gap is even bigger now. .031
 

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don't just insinuate that people just buy HK bolts to fix bolt gap.
I'm not. I'm insinuating that people listen to other people about how bad this part is or that spec is wrong (on their gun) and automatically assume they must start replacing all kinds of parts just because other people have.

One optimistic individual even wanted a list of parts that needed replacing before he even got his gun in his hands... that's sad.

Even GM and Ford use out of spec parts and match them with other out of spec parts to produce a perfectly performing assembly. (undersized spindles to oversized hubs blended with just the right rollers in the cases where I worked in Sandusky). Nothing wrong with the assembly and they are guaranteed for what, lifetime service?

The problem would be when some "expert" says that he had a problem with his car and then someone else reads up on it, figures this is where his squeak is coming from and orders a new part... not a whole assembly. Well, guess what the end result of that would be?

Instead of bringing it back to the dealer to find the actual cause, he's on the path to spending a ton of $$$ and developing a severe attitude towards the company.

See any parallels here?
 

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You make an excellent point SM!

I think the message of "SEND IT BACK" needs to be more dominant on this forum concerning CA guns. I've been telling everyone that I can to send them back and make Todd fix it if they get a lemon off the line. He seems to be making them work on the first or second return now.

The design has more variables than the newb owner like myself realizes at first and we need old hands like yourself to get the message out. :)
 

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Yeah man, I completely agree with you. There is no need to replace parts when nothing is wrong with the parts being replaced. And boy has that been happening recently- a lot. Blindly replacing parts is bad, because many people do not anticipate how all the parts interact together to make the weapon function.

But in this case, I think it's a bit different, considering the nature of the part- the HK bolts are about to be kind of scarce, and the guy found a good deal on one. It's definitely not too much for him to expect it to work in his gun, especially since the guns are advertised (on gunbroker for instance) to "fit all HK parts).

And, take my case- yeah, I could call Coharie up and talk to them about my bolt- but I don't really want to do that. My reasoning for that? Well:

- Yeah, they make cool guns, and they give you good deals on those guns, but honestly, they are NOT the most warm, inviting, nice, people to talk to. That sounds kind of childish, like maybe I shouldn't care, right? Well, it is rather uncomfortable, and the bolt-issue is something I can fix (and fix 100% right on my own without voiding the warranty). Best not to involve extra parties if I can avoid it.

- I bought the gun brand new and it had several problems (major functional issues) for which I returned the gun to them twice to fix under warranty. They did fix it, both times (to their credit). I have seen the quality of their bolts multiple times now, and have lost some faith in them. Hey, I may be mistaken, and just been unlucky multiple times, but what happens happens. Their craftsmanship on most things is good (and damn, they have a GOOD welder) but I have to say, some of their parts are just not good. period.

- I have not done ANYTHING to void the warranty, and I honestly love that they come with a lifetime warranty (that was a major selling point for me). I have used the warranty twice. Given that replacing their bolt head with an HK bolt head does not affect the warranty, and only guarantees me an in-spec bolt head, using the HK bolt-head is win-win (barring any issues like Tabasco here is having, which can be expected for reasons we have already discussed here at length). I just don't feel like taking the gamble and seeing if a 3rd bolt from Coharie will work better. Better to just go with the HK bolt, and KNOW it will be okay.

And now that I'm rambling... it's kind of late... if you've read this far, congrats lol.....
 

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this is a perfect example of incorrect attitude...it seems everyone finally came to the right conclusion, but to be honest, if it aint broke, dont fix it is the best attitude to have...when you buy a coharie, you get a perfectly good gun with a lifetime warranty and todd will honor the warranty...he wont honor it if someone else works on it tho...and slapping hk parts in it for any reason does not necessarily mean it's more cooler...if the gun runs, run it...if it doesnt, send it in for warranty work...what's so hard about that to understand? When my smith and wesson needed a part, i didnt order it from hk...i sent it in to smithy and they fixed it for free...no problems...i just dont get the need people have to "upgrade"...most of the time you better upgrade your migrane medicine cause that's the direction that path is going to take you
 

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it's not always that cut and dry. If it was, this thread probably wouldn't even exist.

As soon as Coharie arms starts selling guns with bolt-heads that are actually made to the proper dimensions, people will stop replacing the bolt-heads.

You can return it for warranty until the cows come home, but it's not going to do **** for you in regard to long-term reliability.

You show me a bolt-head from Coharie that works as well as one from HK, and I will be very jealous, and awestruck- because you won the freakin lottery (literally). It is literally a lottery on whether or not you will get a bolt-head like that from them.

And, if I'm mistaken about that, good God, PLEASE correct me. Man, I would LOVE to be wrong. But I bet you $100 I'm not. That is for damn sure.
 

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Discussion Starter · #20 · (Edited)
this is a perfect example of incorrect attitude...it seems everyone finally came to the right conclusion, but to be honest, if it aint broke, dont fix it is the best attitude to have...when you buy a coharie, you get a perfectly good gun with a lifetime warranty and todd will honor the warranty...he wont honor it if someone else works on it tho...and slapping hk parts in it for any reason does not necessarily mean it's more cooler...if the gun runs, run it...if it doesnt, send it in for warranty work...what's so hard about that to understand? When my smith and wesson needed a part, i didnt order it from hk...i sent it in to smithy and they fixed it for free...no problems...i just dont get the need people have to "upgrade"...most of the time you better upgrade your migrane medicine cause that's the direction that path is going to take you
You have got to be kidding me lol. I can't buy a hk bolt as a BACKUP part and expect it to work? (parts are getting harder to find) Also what are you talking about "when you buy a coharie you get a perfectly good gun"? How many clone threads have you seen in the last 2-3 months regarding issues? 4-5 of us alone had zero bolt gap.

Back on topic, i'm curious to see the difference in dimensions between the hk bolt and CA bolt. I'll bump it when I get some calipers.
 
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