Bolt weight and recoil impulse question?

[sasquatch981]

So I may not be fast on the uptake, and maybe somebody can use simple words to explain it to me.

 

So I have my SBR 9mm set up with a carbine length tube, spacer (5-6 quarters), the waffle spring, a JP .308 spring, and the endine hydraulic buffer.  I currently have a “normal” 9mm bolt with the counter weight still installed.  Shoots great.

 

However, just thinking in simple physics mode, the lighter the bolt, the faster the cycling, and the less weight being cycled, should make for less recoil correct?

 

Just want to make sure I am thinking straight.

 

Thanks.

 

 

[stick]

Felt Recoil or Dot Bounce?

[rowdyb]

f=ma, force equals mass times acceleration. if we're to reduce what you said to simple newtonian physics. want less f? then you need to reduce mass and or acceleration. now how do you mechanically apply that idea to your gun parts?

 

now feel, something subjective..... that's entirely different.

Edited August 24, 2019 by rowdyb

[ck1]

Not to sound snarky, but you probably just have to try removing the weight from your bolt and try it out... There’s just so much variance in the vast array of AR-9 parts out there that IMHO that’s the only way to know for sure...

 

I can say in my Foxtrot Mike AR-9, it ran great with a 6.5oz buffer weight + .308 carbine spring + weight in the bolt, but I wanted both a lighter recoil and less dot bounce... after experimenting with more than a few different things, I ended up with an 8oz buffer weight + .308 carbine spring + weight removed from the bolt (it improved even with the same 6.5oz buffer weight, but ended up liking the heavier one better with the mass out of the bolt): 100% reliability remained, but no contest, the recoil softened and the dot recovered faster, for ME (that’s the important part, it’s gotta feel better to YOU and everyone is different).

It’s worth a try, it won’t take many rounds to feel the difference I bet...

Edited August 25, 2019 by ck1

[BartCarter]

19 hours ago, ck1 said:

... it ran great with a 6.5oz buffer weight + .308 carbine spring + weight in the bolt, but I wanted both a lighter recoil and less dot bounce... after experimenting with more than a few different things, I ended up with an 8oz buffer weight + .308 carbine spring + weight removed from the bolt (it improved even with the same 6.5oz buffer weight, but ended up liking the heavier one better with the mass out of the bolt): 100% reliability remained, but no contest, the recoil softened and the dot recovered faster, for ME...

 

So I am assuming the bolt weight is about 3.5 oz. (CMMG is 3.46 oz for the weight plus the pin) that you removed.  That would make the overall weight change of 2 oz less.  So, three questions:

 

1. Would a buffer of 4.5 oz accomplish the same thing?

2. Isn't it the total weight of bolt plus buffer that should be measured?

3. For final tuning, would it be better to get a tuneable buffer with different weights (AL, steel and tungsten) to finalize what is best for a shooter?

[ck1]

1 hour ago, BartCarter said:

 

So I am assuming the bolt weight is about 3.5 oz. (CMMG is 3.46 oz for the weight plus the pin) that you removed.  That would make the overall weight change of 2 oz less.  So, three questions:

 

1. Would a buffer of 4.5 oz accomplish the same thing?

2. Isn't it the total weight of bolt plus buffer that should be measured?

3. For final tuning, would it be better to get a tuneable buffer with different weights (AL, steel and tungsten) to finalize what is best for a shooter?

 

Not sure how much the Foxtrot Mike bolt-weight weighs that I removed, I'd guess between 2-3oz, but sounds like your CMMG bolt-weight might be heavier... again, all these proprietary AR-9 parts can make one's ideal recipe an exercise in experimentation lol.

 

1. Doubt it, 4.5oz for a 9mm blowback buffer weight seems really light. I have no idea what your Endine buffer weighs... but I was using longer 9mm-specific buffer weights without spacers so my experience is based on those. Plus, you'd just be taking weight out of the end of the stroke, you'd still have mostly the same reciprocating mass for most of the stroke, only with less mass to slow it down...

2. There are more then a few ways guys measure this stuff... I don't know if anyone has the perfect equation. I'm talking a less scientific "shoulder/shooting-feel" test.

3. A tunable buffer weight probably isn't a bad idea if you feel like buying one and really want to play around with it.

 

- My thoughts are this: basically, in my experience it's not so much the total weight, but where the weight is in the system: For me, a lighter reciprocating bolt is noticeably better, but in a way I ended up putting most of that weight back in, but at the end of the stroke with a heavier buffer weight... the mass that moves the most (bolt) being lighter felt better. YMMV

 

FWIW, the JP bolt's that lots of guys love don't have added/removable weights and are usually a couple ounces lighter than most other companies' bolts out there with weights installed... that's worth noting because JP is usually out front on a lot of this PCC AR-9 stuff. So IMHO, removing the weight from the bolt and trying it out like that, is in a way, trying that same "lighter bolt" concept with the gear you've already got.

Edited August 26, 2019 by ck1