Buffers and Springs...

[MikieM]

I took two guns to the range today. I wanted to zero one of them for next weekend's match, weather permitting. The other was to see how they performed with with each having a different buffer, and spring.

The significant differences between the two were weight, barrel length, and buffer/spring combinations. Every thing else was the same, including ammo. I used 124 gr. FMJRN over VN320 powder at a PF of about 130 out of a 10.5 inch barrel.

Gun number one weighed in at 5 pounds,13 ounces and gun two weighed 5 pounds, 8 ounces. Number one had a 16 inch KAW pencil profile barrel. Number two had a Taccom ULW (5.25 inch) barrel. The ULW barrel did not quite make PF, but probably didn't miss it by much.

The gist of all this centered around the buffer/spring combos. Gun one had a KVP heavy (7.5 ounce) SS in a Sprinco AR10 (Orange) Carbine spring. Blitzkrieg says that this spring is slightly stronger than the JP AR10 spring. Gun two was fitted with the Taccom 3-Stage and the spring that was supplied with it.

 

After shooting nearly three hundred rounds through both guns at the plate rack, and targets, my opinion is as follows (bearing in mind, of course, that opinions are like rear-ends. Everybody has one.): Of the two, the first pick was the KVP 7.5 ounce buffer with the Sprinco AR10 spring. It exhibited hardly any dot movement, and felt recoil (at the shoulder) was only a single bump. Smooth and solid.

Gun number two wasn't far off the mark, by any means, but the dot did have more jump. Felt recoil was slightly less mild, and with a bit of rattle. To be honest the shorter barrel and lighter gun weight probably came into play here.

 

Conclusion: I like the heavy buffer and spring. It is a very stable and simple system (nothing really to break), and the weight of the bolt/buffer is certainly enough to ensure safe operation, and correct timing. The Taccom 3-Stage works very well, and I don't believe you could go wrong by using it.

That said,  you might want to give the heavy buffer and stiff spring a try.

 

Thanks, Mike.

Edited January 22, 2018 by MikieM

[stick]

I too will have some tests to run in the near future.  I just installed a Taccom ULW barrel with carbon fiber handguard and a Taccom 3 stage buffer in my daughters PCC.  Her gun went from 7lbs down to 5lbs 10oz.  I also installed a Taccom 3 stage buffer in my PCC.  it weighs in at 7lbs 13 ounces.  I will try the Taccom springs and then I will try the Standard carbine springs.  I really didn't have a problem with the PSA springs and buffer. Like you, I'm curious to see how the gun reacts with different springs/buffer combinations.

[sandrooney]

I just tuned my JP SCS that is in my GMR 15. I went with Eric's set up, (thanks Eric) green spring with 1 tungsten and 3 steel weights.  Big difference from stock. The felt recoil seems more but the dot just stays there, definitely an improvement. 136 PF. Thinking of reducing the PF but may just leave it.

 

[BartCarter]

15 hours ago, MikieM said:

...KVP heavy (7.5 ounce) SS plunger in a Sprinco AR10 (Orange) Carbine spring...

 

Are you referring to the KVP solid SS buffer as a plunger?  Or is this a different product? 

[MikieM]

2 hours ago, BartCarter said:

 

Are you referring to the KVP solid SS buffer as a plunger?  Or is this a different product? 

 

The word 'plunger' slipped in there while I was still half-asleep. I meant buffer.

It was an honest mistake. My toilet over-flowed the other day and I inadvertently grabbed a buffer instead of a plunger. Before you knew it I was knee-deep in shit. 

[RAINY0DAYS]

Curious what your results would be if you swapped buffers in those two rifles. I'm almost positive that you're correct in assuming the ULW barrel is contributing to the feel. I noticed it when comparing my ULW to a PSA build that mine was a bit bouncier. The light weight is still worth it to me, but you do sacrifice some dot movement.

Sent from my Moto G (4) using Tapatalk

[L9X25]

Timing plays a part too, what feels the softest may not produce the best fast-pair.  You may perceive more dot movement but, if the gun returns quickly and is stable, it can provide faster and tighter hits.  

Edited January 22, 2018 by L9X25

[MikieM]

Yes, and I'm not complaining. What dot movement there is seems to come back quickly.

The 5 and 1/2 half pound gun (ULW barrel) is a joy to shoot. It moves like a sports car. Granted, you feel a little more recoil, and you feel and hear the bolt/buffer clatter similar to an AR15, but it's a great PCC.

The shrouded barrel, bolt, and 3-stage buffer system, is all Taccom. I think I'll keep it that way as something to reference from.

[MikieM]

7 minutes ago, L9X25 said:

Timing plays a part too, what feels the softest may not produce the best fast-pair.  You may perceive more dot movement but, if the gun returns quickly and is stable, it can provide faster and tighter hits.  

 

Absolutely. 

The way I look at it is this:
1. Choose the bullet weight you want to use. In my case it's a 147 grain.

2. Find the velocity of that bullet at the PF you want. In my case it's 900 FPS.

3. Calculate the mass (weight) of the bolt and buffer combination based on the velocity, and weight of the bullet. In my case the combo is just a bit over 22 ounces.

Now you have a correctly timed blow-back system that is safe and reliable. All you need now is a spring that you feel comfortable with. In my case I favor the very stiff Sprinco AR10 Carbine. Note: This spring choice, however, could change through further experimentation, but it's a good starting point.

 

 

[Supertrunk]

I'm new to PCC and still tuning (fooling with?) my new build. Would you mind sharing the formula for that bolt / buffer weight calculation?

I went with an all tungsten buffer (4 weights), but bought 4 steel and 4 aluminum weights to tune with.

 

Thanks.

[MikieM]

Although tunable buffers have been around for awhile, my personal belief is that they are unnecessary, and in the extreme, potentially dangerous. Now, this may be bold talk coming from a one-eyed fat man, but in our guns the bolt and buffer move back and forth as one unit. Because of this their combined mass (weight) should be considered when selecting parts. When you tinker (or tune, as you say) with the weight of the buffer you alter the weight of both the buffer and the bolt so again not necessarily a good idea.

In my view the only tunable part of the gun is the buffer spring, which is an easy thing to do. We simply try out different spring rates until we find the one that feels best during recoil. The felt recoil and dot bounce we are all concerned about is relative to the powder charge we are using, but can be somewhat mitigated by our choice of springs.

Remember. The buffer spring only does two things. One: It holds the bolt/buffer assembly in place (if it wasn't there the bolt/buffer would slide back into the spring tube whenever you held the muzzle up). And Two: It returns the bolt/buffer back to battery once the gun has fired.

The formula I used for obtaining total bolt/buffer weight came from Orion's Hammer. You should be able to Google it. Also, Mr. Google can help you solve for the constant in the formula. 

As for the diameter of the breach, I used the diameter of a cartridge head and it worked fine.

Remember. All this stuff is my own beliefs and opinions. There is more than one way to de-fur a feline.

Mike.

[1981Shooter]

16 minutes ago, MikieM said:

Although tunable buffers have been around for awhile, my personal belief is that they are unnecessary, and in the extreme, potentially dangerous. Now, this may be bold talk coming from a one-eyed fat man, but in our guns the bolt and buffer move back and forth as one unit. Because of this their combined mass (weight) should be considered when selecting parts. When you tinker (or tune, as you say) with the weight of the buffer you alter the weight of both the buffer and the bolt so again not necessarily a good idea.

In my view the only tunable part of the gun is the buffer spring, which is an easy thing to do. We simply try out different spring rates until we find the one that feels best during recoil. The felt recoil and dot bounce we are all concerned about is relative to the powder charge we are using, but can be somewhat mitigated by our choice of springs.

Remember. The buffer spring only does two things. One: It holds the bolt/buffer assembly in place (if it wasn't there the bolt/buffer would slide back into the spring tube whenever you held the muzzle up). And Two: It returns the bolt/buffer back to battery once the gun has fired.

The formula I used for obtaining total bolt/buffer weight came from Orion's Hammer. You should be able to Google it. Also, Mr. Google can help you solve for the constant in the formula. 

As for the diameter of the breach, I used the diameter of a cartridge head and it worked fine.

Remember. All this stuff is my own beliefs and opinions. There is more than one way to de-fur a feline.

Mike.

Interesting.  I ran the formula with multiple projectile weights, all pushing around 130PF, keep coming back to 1.7lbs or 27oz.  I couldn't find my kitchen scale this morning, but going off of the manufacturers website numbers, my PSA bolt weighs 15oz and the Taccom 3-stage weighs 6oz, so I'm at 21oz total weight currently.

[MikieM]

I am no whiz kid when it comes to math, but my first thought is: What number did you plug in for velocity?

The accompanying chart shows a bolt weight of 1.7 pounds from a velocity of 1500 fps.

[1981Shooter]

51 minutes ago, MikieM said:

I am no whiz kid when it comes to math, but my first thought is: What number did you plug in for velocity?

The accompanying chart shows a bolt weight of 1.7 pounds from a velocity of 1500 fps.

I changed the velocity for each projectile to match 130PF, so 1130 for 115gr, 1050 for 124gr (which is the load I'm running), and 885 for 147gr.

[MikieM]

30 minutes ago, 1981Shooter said:

I changed the velocity for each projectile to match 130PF, so 1130 for 115gr, 1050 for 124gr (which is the load I'm running), and 885 for 147gr.

 

Try this for the 147 grain bullet: 0.00109 x 147 x 885 x 0.149.

[joelogic]

I switched from a 16" JP to the Taccom ULW and decided to test some springs.  I was running the Sprinco Red with the Blitzkrieg buffer.  Action felt smooth and quick but the breech face was getting battered.  Tried a carbine spring, same buffer, in the ULW and got plenty of bounce.  JP polished carbine spring seemed like the best compromise.  

[MikieM]

1 hour ago, joelogic said:

I switched from a 16" JP to the Taccom ULW and decided to test some springs.  I was running the Sprinco Red with the Blitzkrieg buffer.  Action felt smooth and quick but the breech face was getting battered.  Tried a carbine spring, same buffer, in the ULW and got plenty of bounce.  JP polished carbine spring seemed like the best compromise.  

What load were you using?

Number one on the list of things to do is decide upon a PF number you want. In our case the baseline is 125. Then, build your load around that.

When you have the load you want you'll have the necessary information to find the correct weight bolt/buffer combination. It's all down hill from there. You can then find the spring that gives you the feel you're after.

[Supertrunk]

Thank you for the well thought out answer.

 

Actually, I have that spread sheet, just from another source, so now I can go get the formula. Like some of the other folks, I've been looking at the 27oz. "ideal" total weight, but seeing folks running a LOT lighter bolt / buffer combinations. Many folks seem to be going lighter bolts / buffer / springs successfully, so there's the conundrum...

[joelogic]

That’s true but I was just tinkering with barrel length.  I run xtreme 124s and use 3.8gr of 700x and barely make 125 out of the 5.5”.  I also run 6gr 3n37 for heavy steel and mgm spinners, which clocks 1150fps out of the 16”.  Interestly the 3n37 shot like buckshot out of the 5.5”. 

[MikieM]

1 hour ago, Supertrunk said:

Thank you for the well thought out answer.

 

Actually, I have that spread sheet, just from another source, so now I can go get the formula. Like some of the other folks, I've been looking at the 27oz. "ideal" total weight, but seeing folks running a LOT lighter bolt / buffer combinations. Many folks seem to be going lighter bolts / buffer / springs successfully, so there's the conundrum...

 

I don't think 27 ounces is ideal.

When I did the calculation for my gun I came up with 21.5 ounces total weight for the bolt/buffer. With a Taccom bolt (15 ounces) and a KV buffer (7.5 ounces) I'm close enough for the girls I run around with. Throw in a Sprinco AR10 Carbine spring and this combination works great at PF 130 using 147 grain RN's.

[joelogic]

Is there a spreadsheet or something with these calculations?

 

At full speed I get a lot of right side bounce.  If I hold center A, gun moves right to just outside the A/C perf.

 

Taccom ULW, JP Bolt, Bliztkrieg Aktive buffer, JP 223 polished carbine spring, 124gr RN xtreme, 3.8gr 700x, 1050fps. 

Edited January 23, 2018 by joelogic

[MikieM]

It sounds like bullet torque is causing your problem which seems odd out of such a short barrel (5.25 inches).

Your bolt/buffer combination should be just fine as far as mass (weight) is concerned. 

My only suggestion, at this point, would be to try a heavier bullet with a little faster powder. 147 grain and Titegroup, or N320, say.

[joelogic]

700x is 12 on the list.  Titegroup is 15 and N320 is 25.  I was hoping to not have to go with 147s.  I prefer to only inventory 1 load but I guess I may have to if I am going to chase down a PCC load.

 

Thanks

 

http://www.wwpowder.com/PDF/Burn Rates - 2015-2016.pdf

[MikieM]

8 minutes ago, joelogic said:

700x is 12 on the list.  Titegroup is 15 and N320 is 25.  I was hoping to not have to go with 147s.  I prefer to only inventory 1 load but I guess I may have to if I am going to chase down a PCC load.

 

Thanks

 

http://www.wwpowder.com/PDF/Burn Rates - 2015-2016.pdf

 

You might get a better answer in the 9mm reloading section of the Forum.

I don't think your equipment is the problem. I also have a Taccom ULW that I shoot 124's through and the dot moves vertically. And not by much.

[JAFO]

2 hours ago, joelogic said:

At full speed I get a lot of right side bounce. 

 

When I was using a standard carbine buffer and spring and short-stopping the buffer with quarters in the tube, I got right side bounce, too.  I removed the quarters when I went to a Blitzkrieg + AR10 rifle spring, and I now have vertical bounce.  Eric suggested it may have had more to do with short stopping the buffer than anything else.  Do you have a buffer spacer installed?  If not, perhaps your spring is going solid on you?

Edited January 23, 2018 by JAFO