SR25 + RC2 & Double Feeds, Lube thoughts?

Detroit_1

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Minuteman
Apr 17, 2006
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So I have 16" APC and and RC2 and shoot exclusively hot 175s. For some time now I have been using the KAC buffer (21057 4.5 OZ) and a Tubb flat wire. Now I am not saying my lube regime is correct - in fact, I am pretty sure it is a part of the problem, but I just slather some white grease on the worn areas of the BCG & bolt. Now it seems like I get @ 40 - 80 rounds before I get a one of those fun stoppages - fresh round is caught under the ejected round and it is all caught in the port and the fresh round usually is junked.

Now for the longest time I thought to myself if I just had a magic buffer and spring combo this fat pig could just keep chugging along without creating that bird's nest of shit in the port. I procured a 5.5 oz CAR buffer from Slash plus his spring; a new Tubb spring and no name H2 buffer; the 21057 + KAC spring. So I started out with my grease & the 21057 + Tubb. I think I made it @ 40 rounds or so before the first stoppage. I then left the gun dirty (maybe 60 rounds or so at this point) and started swapping out buffer and spring combos. To me the best was the no name H2 (which is perceptively heavier than the 21057) and the Tubb. None of them were 100%. Total stoppages with all combos and over @ 220 rounds was probably 8 or so. The 21057 & spring were not better than the 21057 + Tubb. The combo from Slash is interesting, the spring is the shortest of the 3 and feels about as stiff as the KAC spring. When shot it seems to exacerbate the feeling of a big freekin BCG sloshing around - like a brief delay before unlock, rapid coiling, a more noticeable secondary impulse over the Tubb, and then rapid uncoiling and bolt lock. The H2 + Tubb chugged along pretty good but was smoother throughout the impulse cycle. Gun runs great with no suppressor even when dirty.

How do you all lube? Is there a point where your large frame chokes?

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Thank you all. I'll work on my lube game. I have gotten away with grease on 5.56 guns for a long time now, but they do not respond quite like the large frame. The volume of gas and particulates must be (exponentially?) higher.

FWIW - I had a 20" at one time and used a rifle length buffer from Slash w/ the KAC spring I had - worked like a charm. The body of his CAR10 (5.5 oz) buffer is too wide to fit the inside diameter of the Tubb spring - otherwise I do wonder about that combo. On his site, Slash advises that flat wire springs are not recommended for any application.

I think there are several ways to skin a cat, and a flat wire spring 'feels' like it smooths out the impulses a touch. However, I personally don't claim to know if it is the correct thing to use or not, but if Sinister says thumbs up - that is a very strong rec in my book.

Again, thank you all.
 
No grease. Consider moving to a KAC PRG suppressor on your APC. They are widely available and cheap nowadays. If you go this route then you can put the OE KAC spring and buffer back in like the gun was designed to run and all problems disappear. Added bonus of a much nicer mounting solution than the RC2. Also, your BCG won't look like something out of a Mad Max movie after a few rounds.
I have an APC and a PRG can and have never had a malfunction. Yet.
 
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Consider moving to a KAC PRG suppressor on your APC. They are widely available and cheap nowadays. If you go this route then you can put the OE KAC spring and buffer back in like the gun was designed to run and all problems disappear.
This is the most correct answer. RC2 is overgassing the SR25. Addressing that from the backend is a bandaid at best, addressing it from the front end is ideal.
 
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There is no place on an AR15, other than when used for assembly, for grease. In fact, if you're going to be running more than 100 rounds between cleanings, using grease is likely accelerating wear. Lower viscosity lube works best in an AR because it flows and the cycling of the action allows the lube to displace crud as it builds up. Grease keeps the crud where it is and essentially becomes lapping compound as it mixes with hard particulates.

There is nothing complicated about lubing an AR and it doesn't take some special concoction that you have to mix at home to get it done. Find yourself a reputable synthetic lube, like Slip 2000. A drop or two on the charging handle, a drop or 3 on each of the rails of the bolt carrier, a drop on the cam pin shaft, a drop for the extractor and ejector and a couple drops in the vent holes for the rings. Wet the bolt lugs and you're done.

If your setup was running and stopped running when you added the suppressor, it's probably because you're way over gassed. What you're describing sounds like very excessive bolt carrier velocity. Instead of tearing your hair out with with buffers and springs, why don't you just install an adjustable gas block. Turn down the gas to increase the closed bolt lock time. This will result in less bolt velocity.

Either turn the gas down or go with a low back pressure can.
 
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Instead of tearing your hair out with with buffers and springs, why don't you just install an adjustable gas block. Turn down the gas to increase the closed bolt lock time. This will result in less bolt velocity.

Either turn the gas down or go with a low back pressure can.
It’s a proprietary gas system. The only real answer is the can.
 
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I doubt that the issue you're seeing is due to use of grease. Sounds like your ejection force is not adequate for whatever speed the surefire is adding to bolt carrier velocity.

As far as the lube procedure for SR-25s go, we recommend using a MIL-PRF 63460F approved product, such as G96.

Recommended courses of action:

1: Confirm that the rifle functions properly with the KAC spring and buffer unsuppressed.
Failing that, contact KAC. If it doesn't run in the baseline configuration you have a problem with the unlocking/extracting/ejection parts of the cycle of operation. Frankly, this sounds like a sticky ejector or a broken ejector spring. Might be worth putting a few drops on lube pooled up around the ejectors and do a few hand-cycles with a brass punch or spent cartridge.

2: If you really want to play the buffer and spring swap game, definitely make sure that the buffers that you use are of standard length. Using a shorter buffer will result in impact of the carrier into the forward edge of the receiver extension.

3: Swapping suppressors to a low-backpressure design will definitely reduce backpressure compared to what you are using now.

All of that said, my first check would be the ejectors.
I know of quite a few people that use the KAC H2 buffer with a Tubbs flatwire spring and are getting good performance.
I can't say with 100% certainty that the issue is the ejectors, but it's the first thing I would want to eliminate as a suspected cause.
 
Thank you JackL; and I think you're right - I have inconsistent ejection from the 12 to the 3 and most sort of dribble out. Gun runs great w/out the SF can, even really dirty.

My ejectors move freely but I do notice a slight difference in spring tension between the 2.

I did put a rubber O ring on the extractor spring (have not tried it out yet) but I don't think it can hurt.

Yes - at some point I should probably break down and buy a KAC can.

Thank you all again.
 
Thank you JackL; and I think you're right - I have inconsistent ejection from the 12 to the 3 and most sort of dribble out. Gun runs great w/out the SF can, even really dirty.

My ejectors move freely but I do notice a slight difference in spring tension between the 2.

I did put a rubber O ring on the extractor spring (have not tried it out yet) but I don't think it can hurt.

Yes - at some point I should probably break down and buy a KAC can.

Thank you all again.
That rubber o-ring can be a problem. Use the stock bolt as supplied. Ejection is a balance of ejector force as well as extractor force, changing one without compensating the other can lead to problems.