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Discussion Starter · #1 ·
New PTR91 owner here, haven't been able to find an answer on the Forum about my questions:

1. What should my expectations be for barrel life?

2. Is it recommended that the bolt and locking piece get changed out as well when the barrel is as it is in the AR world?
 

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First, welcome to the forum. As with any barrel, how will it be used and what are the expectations, will effect perceived barrel wear. Will your rifle be used in a full auto personal or rental application? Or would the typical use be shooting slow fire at 600 yards +? Or are you shooting more like 50-100 yards with occasional semi rapid fire for a mag or two? Do you clean regularly? A dirty barrel can make a low miles barrel shoot or function terribly. Not only does the bore need to be cleaned, the chamber flutes must be cleaned or the gun will have function problems.

My limited understanding is a steel or stainless steel buttoned rifled barrel with mostly slow fire use and good maintenance has reasonable accuracy for somewhere around 8,000 to 10,000 rds of use before accuracy deterioration becomes pronounced. Accuracy deterioration will tend to show up at greater distances or with more rapid fire, as increased barrel temperatures seem to increase the amount of wear per round. Hot steel is softer than cool steel.

This is not a locked bolt system. Roller delayed system is "semi locked". There is wear as the bolt face hits the chamber end of the barrel. As the wear allows the rollers closer to the barrel face, the bolt gap (please search how to check bolt gap if you don't know how) will diminish. Factory tolerance is 0.010" to 0.018". There are larger sized rollers to get the tolerance back to spec as the action is worn.

In the Rick James book of the MP5 a factory gun wore to the point that the largest factory rollers (8.04 mm) would not get the bolt gap back to the minimum spec. The gun was owned by the Kennedy Space Center and used strictly for training. It had over 500,000 documented round of use. Of course it was used in CQB training and had very little rifling left. Most recreational shooters don't put 1,000 rds a year through any one gun they own. Owners that shoot great distances will tend to change barrels more often as they need a higher level of accuracy. As a barrel change in a roller gun is beyond most collectors, I would think if you feel the need to have your barrel changed, the smith doing so could recommend what should be replaced at that time.

There is pages and pages of information about these guns here. The search function in the upper right hand corner is your friend. I highly recommend it's use. I'm sure with a case or two of surplus G3 mags and a couple thousand rounds of ammo, even in semi you could ruin a barrel in an hour. Take care of it, and it will last you a life time.

Scott
 

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For 7.62x51 barrels, my experience has been that given moderate amounts of rapid fire, barrels lose their ability to group well at 600 yards at about the 5000 round point. At that point, there are occasional fliers way high and low at 600 yards, but I don't see them at 200 and 300 yards. At 200 and 300 yards, such a worn barrel will still shoot about the same score, but there will be less hits in the very center of the target (X ring).

If you are only going to shoot at 200 and 300 yards, you should have meaningful accuracy for several times that many shots.
 

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Since PTR no longer uses real surplus HK, FMP, EBO, or Rheinmetall bolts, who knows how long their USA bolts will last? They seem to be the weak link of their guns, unless they are getting them from RCM, which I don't think is happening. GARY
 

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I concur with the other commenters. PTR barrels are made from 4140 grade steel blanks that are button rifled. Which means about 7000-10,000 round life span, depending on usage. The bolt is made of 8620 steel, heat treated, and should last much longer, 15,000-20,000 rounds. But ! I don't know of any documented tests, so there is no definitive answer.
 

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Discussion Starter · #6 ·
Thanks Gents, about what I thought.

I will keep an eye on the bolt gap as I get more rounds down range. After install of the new HK bolt and locking piece I was at .4mm prior to first round/break in. Didn't get to the range this weekend as the weather didn't cooperate, so I will check again after 200 rounds or so.

Looks like I will have a couple of years to find another barrel and someone to put it in. Probably shoot 5000 rounds a year, but nothing full auto.

Find it interesting that in 6 years in the Infantry in the Corps, we never ever shot full auto/burst, unless of course it was an M60 or SAW.
 
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