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Discussion Starter #1 (Edited)
I have noticed that the top "Hood" (that overlaps the top of the bolt head) of the trunions on the Hk93/33's with 1in7" twist are longer than the 1in12" twist trunions? Any one know the reason behind this?

If you guys don't know what I am talking about, I can post some side by side pictures. Added below.

thanks,
Kenw45
 

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Discussion Starter #5 (Edited)
Sorry my pictures are not as nice. Please don't let the sheet metal on the left distract you. As you can see the one on the right has the longer hood than the one on the left. The bottoms are the same length unilke ptoguy's pictures above.



I wonder if in the HK93's this was done for pressure reasons. The older 1in12" guns were marked 223 and the 1in7" guns (only imported 1988 & 1989) were marked 5.56 on the receivers. 5.56 is a higher pressure round. Only problem with that theory is that the two trunnions above came out of HK33 15.5" guns. They should all be 5.56 if they are military. Only other thing might be the change over to the use of the 62gr round (hence the reason for the 1in7" twist). Not to up on the 5.56 ammo specs. Is the 62gr M855/SS109 longer or have a higher pressure than the older XM193- 55gr?

Or was this just one of those small unnoticed upgrades that Hk did along the way in the manufacturing process.
 

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Discussion Starter #8 (Edited)
The one on the right is a British proofed "IF" date coded Hk33 and the one on the left not sure... maybe a Maylasian ????
 

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I can't see that difference being due to a minor change in ammo. I'm comfortable in saying it was a change in production at HK as an improvement or update to improve and make the product better. Can't say that it would make one iota of difference to me either way.
 

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Discussion Starter #10
I wonder if G3Kurz Knows why they are different.

If the trunion is the same specs as far as the barrel fitment and rollers. Can you put a 1 in7" barrel into one of the older (shorter) trunions without any issues (feed, pressure problems, etc). I mean I don't see why not, but why the changes by H&K on the newer twist guns?
 

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I'd like to see G3k comment on this also. I wonder if the difference is just a coincidence in that the trunnion was changed just as 1:12 fell out of favor to the 1:7. Is there a way to see at what serial range the new trunnions started to appear vs when the change to 1:7 was made?

kenw45, I don't see why the barrels can't be swapped between trunnions. If the bore of the trunnion is the same ID and length that's all that matters.
 

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Curious, does anyone know what pattern the US made 5.56 trunnions follow? Long or short?
 
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