Long stroke SureFire Carrier

[Spart]

Maybe this is a dumb question, but will the long travel cause bolt catch problems? I’m thinking about 9mm ar’s needing a spacer or longer buffer to prevent that.

A good possibility? Bolt catch quality varies.

I actually run a mild overstroke setup in my 3-gun rifle and haven't had any issues. I have a Seekins catch which is milled rather than MIM or whatever, not sure that it matters.

[vicious_cb]

$399!?

And I thought LMT e-carriers and bolts were cost prohibitive. I can almost go through almost 6 mil-spec bolts for that price.

[LDB]

I don't get it but it's interesting and something to work on learning about.

[Biggy]

I don't get it but it's interesting and something to work on learning about.

It is mainly about increasing the rifle reliability, but there are also quite a few other benefits to it.

[MQ105]

The overstroke setup is something that's not offered anywhere else...

Run a carbine length buffer in an A5 RE... ? I may try this...

I also wonder about bolt catch longevity.

[1168]

Run a carbine length buffer in an A5 RE... ? I may try this...

I also wonder about bolt catch longevity.

Gas key will bottom out in the charging handle. Maybe there is a correct number of quarters you can stack in there. Probably need to use a carbine spring, too. Let us know how it goes if you try it.

[MQ105]

Gas key will bottom out in the charging handle. Maybe there is a correct number of quarters you can stack in there. Probably need to use a carbine spring, too. Let us know how it goes if you try it.

Nope. Because of the gas key location, there can be no further rearward movement of the BCG. Thus, the reason for Surefire's gas key mod on their BC. I wonder if a standard buffer and A5 RE will work with the SF OBC...? We'll have to wait until release, I guess.

[Spart]

Run a carbine length buffer in an A5 RE... ? I may try this...

I also wonder about bolt catch longevity.

Bad idea. If you look closely at the SureFire carrier, it's been modified to be able to go deeper into the receiver extension without any clearance issues. You're talking about a 3/4" difference between carbine and A5 buffers. Don't do it unless you want to damage your lower receiver and receiver extension.

Gas key will bottom out in the charging handle. Maybe there is a correct number of quarters you can stack in there. Probably need to use a carbine spring, too.

Actually the first thing that bottoms out is the back of the carrier key against the lower receiver ring for the receiver extension.

Let us know how it goes if you try it.

Get ready for a huge post, because I've been playing with this for a few years now!

I haven't fully developed this concept. It's probably going to be the subject of a detailed video on my channel down the road. And I can't claim any originality on it, although I did start playing around with it well before I ever saw the InRangeTV video on Jim Sullivan or read his patent. It's not a new idea in general, just one that hasn't been commercially applied to the AR15 until now. But I do respect the work that has gone into perfecting it by Mr. Sullivan for his use cases (full auto + suppressed fire.) Obviously, someone trying to commercialize this is going to run afoul of that patent and the attorneys of ArmsWest or Surefire.

That out of the way, here is what I've done for a MILD (when compared to the Sullivan/Surefire design) overstroke system on a gamer semi-auto gun.

On my 3-gun rifle, I have always used a Vltor A5 receiver extension and lightened A5H0 buffer. When I first set this gun up with no overstroke and the gas tuned to just barely lock it open, it wouldn't cycle properly if you fired with the stock out of your shoulder. You'd get a bolt over base malf about 50% of the time and it wouldn't lock open. That's how finicky this stuff can be when you're pushing things to the edge of not working - just not having the gun in your shoulder was all it took to go from working to not working.

So I got to thinking about how to increase the reliability without sacrificing secondary recoil mitigation. If you're a 3-gun gamer, you don't want to feel that secondary recoil impulse from the BCG+buffer heavily bottoming out in the receiver extension.

The first thing I did was setup the gun with the receiver extension one full rotation out from fully screwed in. This necessitates running without the buffer retainer. I believe you can do this on almost any AR with a carbine receiver extension and not run into clearance issues. But it allows just a little extra stroke for the reciprocating components. FWIW, I'm a firm believer that the buffer retainer is there to keep Joe from putting his buddy's eye out, and can be a liability. I've seen them break and render a gun non-functional. So I have no qualms running without that thing.

The next thing I did after running like that for a while was trim the bumper on my A5 buffer. I removed about 0.066.



Keep in mind that 0.066 is not a number you should use! What you need to do is check the clearance between the back of your carrier key and the lower receiver, and leave some wiggle room there. I believe that Jim Sullivan's patent mentions that the buffer bumper can compress 0.040. I left 0.056 of clearance, so you could potentially take it further than I did.



This took me from around 0.154 between the bolt catch and the bolt face at the limit of rearward travel to about 0.238. And if you can't tell from the pics, that "before" measurement is actually on a different gun - one of my other rifles with an unmodified A5 setup. So that's about a 50% improvement in the distance between the catch and the bolt at maximum travel. That's giving the magazine more time to feed and the bolt catch more time to pop.



This has worked out swimmingly. Now the gun can be fired one-handed with no shoulder on the stock and it locks open. (Not that you should do that, but just a way to demonstrate reliability.) Recently, I even tried it out cold soaked in -18°F temps and it functioned fine - see the video at the bottom of this post. By the seat-of-the-pants feel, it seems to have a slightly less jarring recoil impulse than it did before doing the overstroke mod. Is it a panacea? No, this gun won't function on lower powered ammo. Hell, I tried Winchester "5.56" and it doesn't have enough oomph to cycle the carrier fully compared to my staple of Wolf Gold .223. I attribute this to adjusting the gas to run the bolt as softly as possible more than anything. That's just something gamers have to be aware of - you tune the gun to run on one load, and other loads with less power may not work. I think an overstroke system gives you more "slop" when it comes to this sort of thing, and going from my setup to one with overstroke similar to the Sullivan/Surefire design would probably net you operability with a wider range of loads while maintaining the least recoil impulse possible.

I want to reiterate that my goals are different from the Surefire OBC and Jim Sullivan's ideal. Heavy mass components can be great in a full auto because the tertiary recoil impulse (the carrier+buffer slamming forward into the barrel extension) is immediately counteracted by the primary recoil impulse (the bullet leaving the barrel.) And the Sullivan/Surefire setup mitigates the secondary recoil impulse (the carrier+buffer slamming into the back of the receiver extension.) But I'm not concerned with full auto controllability - this being a semi-auto only 3-gun rifle, I can't take advantage of full auto fire mitigating the tertiary recoil impulse. So instead, I have a finely adjustable gas block, lightweight JP carrier, and my A5 buffer has only one steel weight with a delrin spacer where the other three previously were. So whereas it was an A5H0 buffer, you could say it's now a A5 minus 3. The tertiary recoil impulse is still there, but diminished because the parts are significantly lighter. I have no particular reason for running with only one weight vs. a fully gutted buffer (like many gamers do) other than that I wanted to maintain a slight deadblow effect. Someday I might test out other buffer setups if I ever get around to developing a more objective test.

A brief aside - I'm aware that there are two camps when it comes to making a rifle "shoot soft." One camp (let's call it the tactical camp) usually leans towards heavy buffers and full mass M16 BCGs. I think the majority on here fall in this camp. The other camp (let's call it the gamer camp) usually leans towards lightened or gutted buffers and lightweight bolt carriers - sometimes even made of aluminum or titanium. The disconnect between these two camps, in my mind, is the preference for running with a fixed gas block and generally mil-spec gas ports vs. the preference for running a finely adjustable gas block. The tactical camp also has the perceived need for full auto reliability. I say perceived, because it seems like most of those guys in the tactical camp have semi-auto rifles. If you're not Jerry Miculek, you're not shooting 0.09 second splits, you probably don't need to mitigate bolt bounce. Anyway, heavy buffers are a mitigation for bolt bounce but end up getting used instead (even if the user doesn't realize what they're doing) as a mitigation for overgassed rifles. An M4 or M16 should be slightly overgassed to my way of thinking. This ensures the rifle can function in cold temps or when heavily fouled. Yes, your rifle might seem to shoot softer if you toss in a Vltor A5H4 - but you're probably sacrificing some reliability at the extremes of operation. That sacrificed reliability is the same thing that the tactical camp complains about when it comes to the gamer camp's use of lightweight buffers and carriers. The beauty of the Sullivan/Surefire design, to me at least, is it should allow an M4 or M16 to run slightly overgassed without having a jarring secondary recoil impulse. Reliability and controllability all in one.

And I don't mean to denigrate anyone. I have rifles that would put me in both camps. But if you're in the tactical camp and you're not sold on the idea that lightweight buffers and carriers can work - just take a look at how flat my gun runs in the video below. Used correctly, they do work and on semi-auto, they can be fantastic. I fully accept that lightweight reciprocating components on top of adjustable gas can be deleterious to reliability. I'm sure many of you know this. I don't run this setup in my "serious" rifles - those all (for now) have fixed gas, M16 BCG's, and Vltor A5H2s.

Now for that cold weather test:



In that video, the first two rounds cycle fine but don't lock the bolt open. The next ten round mag cycles fine and locks the bolt open. Keeping in mind this is a cold soaked gun and ammo, and it's heating up the more you shoot it.

I do wonder how much the first failure to lock back had to do with the oil I was using. I had previously tried this same test on an approximately 0°F day (gun and ammo cold soaked to the same temp) and it locked open after the first two rounds. But importantly, the action felt slick and normal. In -18°F, it felt a bit sticky.

Also, the rifle in that video hadn't been cleaned in maybe 500-700 rounds leading up to that test - it just got oiled now and then. So it was dirty on top of being -18°F.

And lastly, for those wondering about bolt catch longevity. Obviously, my setup doesn't compare to the Surefire/Sullivan design in this regard. Not only do I have less overstroke, but my components are lighter. I haven't had any issues though. I run a Seekins EBC, which is milled rather than cast/MIM or whatever. It's not very expensive to boot.

[Rayrevolver]

Very interesting.

Even with an adjustable gas block I ended up using an A5H4. I only had a A5H2/3/4 and the fidelity of the gas block didn't lend to fine tuning of buffers. My thought process for more mass has to do with overall reliability even in semi with things like stripping rounds off mags, dirty gun, and tiny bit of slowing the bolt unlocking during suppressed fire.

I wonder if I had made an A5H0/1 I could have used 1 less gas click and settled on a lighter buffer. Maybe a project I can tackle down the road now that I have spare buffer parts.

[BufordTJustice]

Very interesting.

Even with an adjustable gas block I ended up using an A5H4. I only had a A5H2/3/4 and the fidelity of the gas block didn't lend to fine tuning of buffers. My thought process for more mass has to do with overall reliability even in semi with things like stripping rounds off mags, dirty gun, and tiny bit of slowing the bolt unlocking during suppressed fire.

I wonder if I had made an A5H0/1 I could have used 1 less gas click and settled on a lighter buffer. Maybe a project I can tackle down the road now that I have spare buffer parts.

When using the LMT e-carrier, Vltor A5 system, tubbs flat wire AR10 spring, and an SLR gas block, using several verified 5.56 NATO chambers, A5H0 buffer did not permit a smaller gas block "port" adjustment than the A5H4 buffer. In fact, on my suppressed 11.5" Sionics RGP and BRT 16" OPTIMUM intermediate gas barrel with the above setup the A5H4 permitted a smaller gas port setting on the gas block than the A5H0 or any of the other buffer weights (I tried all of them on all of my uppers, suppressed and unsuppressed). Yes, you read that right.

The A5H4 permitted me to run less gas than the A5H0.

I appreciate the few posts above showing lots of experimentation, but there is more going on here. Period.


Sent from my iPhone using Tapatalk