Need help. Recently added an M4 2000 to 10.5" AR upper and I am experiencing short stroking of the the bolt where it catches a new round just barely on return and it slams into the side of the round as it tries to chamber the round. I have used PMC 55 Grn and Federal 55 Grn rounds with the same results. I loaded custom loads with BLC2 with 26.9, 27.4, and 27.6 Grn of powder and a 55 Grn spire point bullet and still had problems. On the gun I replaced the gas rings, tried a different bolt, and a lighter buffer. The only change that helped was going to a lighter (standard) carbine buffer. Any help is greatly appreciated. Thanks...

Does it cycle unsuppressed?

I think you need to go the other direction and add a heavier buffer along with maybe a stronger action spring.

I am also curious if it runs fine unsuppressed. If so...

Sleeper362 wrote:I think you need to go the other direction and add a heavier buffer along with maybe a stronger action spring.

This usually will fix the issue you are talking about.

Yes, it works fine without the suppressor installed. If a heavier buffer is required then the only option I see is the T3 buffer from Spikes. Not sure where or what to get for a heavier spring. Any ideas where to get this? Thanks...

Just get a standard H3. The Spikes buffers cause more issues than they solve in SBR's.

J Krammes wrote:Just get a standard H3. The Spikes buffers cause more issues than they solve in SBR's.

This!

H3.


What you are most likely experiencing is not short stroking, but cycling speed that is to high (from the extra back pressure).

Couple things to try (in order of how extreme):

1. H3 Buffer

2. New GI Buffer Spring (potentially a non-spec stronger one, but then you might run into issues with unsuppressed use)

3. New mags/Mag springs (Might better "Keep up" with the cyclic rate)

4. A switchblock

Thanks guys for the response. As a novice SS guy I appreciate the help. The mag that I was using was a Magpul 30 rd mag. I will place the order for a T3 buffer and stronger spring. Also in response to that last response; what is a switchblock? Thanks in advance and please excuse my ignorance

rsedam762 wrote:Thanks guys for the response. Thanks in advance and please excuse my ignorance

Not a problem. You have to learn somewhere. Just DO NOT go with the Spikes buffer. Go to Bravo Co Mfg. and order an H3 buffer. You can get a new spring, but I think an H3 will do. If you do get both, try one at a time. Both may be to much and cause similar issues. Just curious. What is the make of the upper or barrel? Also, are you using a full auto bolt carrier group.

Thanks for the input, all is appreciated. Upper is made by Rogio and the barrel is Daniel Defense.

rsedam762 wrote:Thanks guys for the response. As a novice SS guy I appreciate the help. The mag that I was using was a Magpul 30 rd mag. I will place the order for a T3 buffer and stronger spring. Also in response to that last response; what is a switchblock? Thanks in advance and please excuse my ignorance

Switchblock is a two-position gas block made by Noveske- a regular and a suppressed setting (prevents over-gassing when suppressed).

http://noveskerifleworks.com/cgi-bin/im ... gi?cat=157