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Recoil Tuning Issues


cmanbrooks
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Hey guys, long time lurker, first time poster. Before I get into the nitty gritty, I want to thank everyone on this forum for all the info I've selfishly gleaned without thanks over the years. It's been a tremendous help in starting my competition addiction.

 

Background 

I've recently built a 3gun dedicated AR after using a Noveske for the past few years of matches. This was supposed to be a "dream build" and to replace the Noveske I had forced into a "do all" role. That being said, I had the latter tuned for very soft recoil with the advice of y'all here. AGB, (slightly) lightened BCG, JP SCS with some weight removed, etc. However, this new rifle...maybe I've been expecting too much of it, but after a few hundred rounds, the impulse just feels harsh in comparison. I realize that this is probably due to a faster cyclic rate, but unfortunately there is a good deal more dot movement as well. I was hoping to get some input from the experts here on what I may be doing wrong, what I should tinker with, or if I should just abandon the project entirely.

 

New Build Details- From tip to butt

-Precision Armament Hypertap .223

-SOT 14.8 AGP SS barrel w/ rifle length gas

-JP 2-piece AGB

-Coda CF HG

-Wilson Combat Upper

-2A Armament Titanium Adjustable BCG

-ADM Lower

-Triggertech Adjustable Trigger

-JP SCS

-XLR Stock w/ tungsten weights to bring overall weight up to ~9lbs

 

Nitty Gritty

Now, to save y'all time, I'll try to briefly explain what I've already done as far as tuning. After the first outing, I had to open up the gas port a bit, as with the gas fully open, it still wouldn't cycle properly with such a short dwell time--even with m193. As I don't have pin gauges, using a drill bit, I'm guessing it's somewhere in the .085 range. She cycles now, but the gas adjustment screw is about 27 clicks from fully closed. Gas adjustment on the BCG is fully open, and will stay there until the port inevitably erodes to the point I want to tinker with that calamity. Brass ejection is at about 1:30-2:00. Obviously overgassed (sharp recoil impulse aside), but its literally 2 clicks from short stroking to ejecting and locking back. 

 

As for the SCS, I have all the weights removed with a plastic spacer and was using the 80% (lightest) spring. Tried the SCS from my Noveske which has 1 steel weight and two spacers with the 80% spring. About the same impulse. I'm cautious to add weight back into the system, but that's my next step in order to decrease the initial carrier velocity. During my latest rain-man workbench session, I decided to replace the JP urethane buffer with one made from 70 duro Sorbothane (adjusted to make sure no carrier key strike w/full travel) and installed the 85% spring with some coils cut. No idea how it'll run, but the idea is to increase the duration of the first impulse.

 

Could it be that I'm just too used to the slow, heavy impulse of my old rifle? I realize all this tinkering is needless more often than not, but I can't help myself sometimes. God help me if I ever get into the PCC game 😅

 

 Thanks for the help and I look forward to any feedback/guidance y'all have to offer!

 

 

 

 

 

 

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Sounds pretty similar to my main match stick. Titanium carrier, 16" rlgs barrel, Hypertap, 80% spring, adj. gas, and taccom plastic buffer, 9ish pounds. Had all the parts to build a clone rifle with the same 14.8" barrel you have, but got a great deal on a Stretch15 instead. I have the same narrow operational window with regards to the gas block adjustment.

 

Without a doubt the ultra light parts make for a very snappy rifle, way more so than the intermediate and mid gas barrels I've had with similar systems. The recoil impulse almost doesn't exist but it still could be described as a bit harsh just because of how fast it runs. I haven't noticed the extra dot bounce you have though. 

 

For giggles, why don't you shoot some pairs on paper at say 20 yards with both rifles back to back. With my more regular rifles I can death grip them or free recoil them and patterns stay fairly consistent. With my tuned up rifles if I free recoil them the snappy recoil puts holes all over the paper, but if my technique is on point it stacks pairs like a milspec rifle never could.

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@TonytheTiger

Just the guy I was hoping to hear from! There's a reason our builds are similar, you're on just about every LW/recoil mitigation parts post on here 🤣. Glad to see I'm not the only one with a narrow optimum gas window. Do you have the same issues with brass ejection pattern? 

 

I would think the adjustable gas would take care of the snappiness of the rifle, just due to the fact that less gas should be required to run the lightweight parts. That's one area of theory where I still find a disconnect. The whole point of adjustable gas is to bring carrier speed down to a similar velocity as milspec or full weight parts isn't it? Any thoughts as to why the impulse is so distinctly different given the above?

 

I'll definitely give that a shot. It won't be apples to apples, with Noveske's "medium" contour pig of a barrel, but will provide noticeably different results I'm sure. Could the weight distribution cause more muzzle rise as well? I've got the center of balance roughly around the trigger guard. The stock is set with the recoil pad about an inch below the buffer tube as it gives me the best stock to shoulder contact. Going to raise that up inline with the receiver extension and see if reducing that fulcrum point helps as well. Thanks for the insight!

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My 16" rlgs ultra low mass components rifle ejects around 2 o'clock, and adjusting the gas block puts it into no lock back mode, just like yours. The 15" intermediate with low mass parts is much more agreeable, 3:30 ejection, feels like lower carrier speed, but damn if it just wont stack doubles like the other rifle even if it feels more tame.

I think the titanium carriers and plastic buffers are just so light that even with the minimum gas required to run they just cycle crazy fast anyways.

 

Weight distribution and stock setup absolutely play a part in perceived recoil. Every time I change barrels I get them a little lighter and the increasingly rearward balance seems to make things jumpier up front till I subconsciously recalibrate to it. Way more so for stock setup. Whenever I want to make a rifle behave like my match rifle I buy a Odin Zulu, measure all the dimensions and then copy it exactly to the new stock. I eyeballed it once and the new rifle behaved terribly. Duplicated my normal setup exactly and suddenly the stars aligned and the rifle shot great.

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14,5” barrel witha rifle gas system means a very short dwell time.  You have a lot of gas in a short period to get the bolt moving.  Thats not ideal.


adjustable gas can’t slow down a light carrier+buffer.  The springs and mass will dictate the carrier speed to get a full stroke.   All you can do with the gas is remove excess gas beyond what it takes to cycle (which slows it down some), but the carrier speed won’t ever be as slow as a full weight system.

 

hard to guess how your specific reciprocating mass and springs are interacting, you have some fancy pants parts in there, but just like pistols, light rifle builds are going to kick a little more than heavy rifles just from the mass of the rifle versus the velocity of the projectile.

 

I enjoy shooting my 5lbs build in competition, but its a very different experience to my full weight 18” SPR.  The SPR is much flatter and double taps very efficiently.  My LW build handles very very fast, and has a very fast 3gun trigger and carrier speed, but has more recoil to manage.   Its net neutral for me.

 

 

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