PCC Reoil / Bounce

[StealthyBlagga]

I forgot to mention that I started THIS THREAD in the summer, which shows how shortening the recoil stroke can reduce muzzle jump and significantly improve shot-to-shot times. I hope it is informative... maybe a Mod can migrate it over to this forum.

[Aircooled6racer]

Hello: I tested out the AR 9mm build today. I am using a 308 spring with the 5.4oz buffer and a shim in the back to regulate the movement of the bolt carrier to just about 1/4" past the catch. The bolt locked back every time with this setup. The loads are a little hot still at 140.9-148.2PF using 115 and 124 grain bullets. The 124 were the hotter loads I use for a pistol. Going to try 3.5 grains of Tite Group with 115 grain bullets and see how that works. After I get the load, I will work on the buffer setup. Keep the great info coming! Thanks, Eric

[ChuckS]

Got a chrono baseline this morning. 16" barrel with Frontier 124 RN 1.137"

1) 4.0 N320 - 142

2) 3.8 N320 - 136

3) 3.3 N310 - 130

4) 3.1 N310 - 125

After shooting 100 rounds in practice with my open pistol, I didn't know #1 was stout until I got to 3 & 4 gonna try 3.6 of N320 since I have more of that powder than the 310 and want to save the 310 for some nice .45 loads. Now to see if the light loads will cut it at match speeds...

[Aircooled6racer]

Hello: You must have either a slow barrel or a batch of slow N320. I think 3.0 grains of Tite Group with 124's should be about 130PF and N320 is usually about the same charge weight. Thanks, Eric

[Aircooled6racer]

Hello: I chronoed some today using 115 grain Acme bullets. 3.3 grains of Tite Group, Winchester small pistol primers, 1.150" OAL gave me 131PF out of a 16" KAW barrel. Very accurate and soft shooting. 308 buffer spring and 5.4oz buffer. I still need to do more testing but it is raining here now but we need the rain in Georgia. I am going to try some 121-125 grain bullets and maybe even 147-165 grain. Thanks, Eric

[Cavy]

On 11/27/2016 at 6:42 PM, CZ85Combat said:

The AR 15 white spring is the 80%  spring.....

• JPSCS-SPRING15-80: 1 side white
• JPSCS-SPRING15-85: 1 side black
• JPSCS-SPRING15-90: 1 side green
• JPSCS-SPRING15-95: 1 side yellow
• JPSCS-SPRING15-100: no color

Thank you! I was not sure what you meant by 80%. I am trying to sort mine out. Appreciate the input.

[cking]

First observation, most carbine length buffers suck. The worst are the solid ones. Then make the gun feel lousy and make gun bounce worse. Most 9mm bolts are fairly heavy dictated by the nature of blow back. But the space available makes them still too light in AR. So everybody puts a heavy buffer in. Problem also that carbine buffer doesn't leave enough room for the buffer to work like the ones in a rifle.
A Rifle buffer is made of light metal, with heavy weights inside that have lots of room to move.

Movement is the key what I call decoupling of reciprocating weight.

When a bolt is closing the weights help with bolt bounce, but they do something else more important. In a 9mm the bolt doesn’t have the floating rotating bolt carrier design to prolong an eat up energy rotating/locking the bolt. It is just two pieces of metal slamming into each other, thus the forward down pitch of 9mm’s which cause dot bounce. Solid buffers make this worse. More weight stopping quickly/abruptly.

So back to the rifle buffer, as the bolt is closing driven by the recoil spring when it finally comes to a stop. The amount of weight that stops is not the total weight of the buffer, bolt/carrier, and spring. The weights inside the buffer are still moving forward and thus do not contribute to momentum that is converted into felt energy. Eventually they will finally stop, and contribute to the total energy but the time delay greatly reduces the felt impact. So they stop bounce by reducing the effective weight and then delivering delayed impacts to counter the bounce. Upon firing the weights are forward and contribute to the total mass of the inertia needed to be overcome to cause bolt rearward movement.

So the 9mm carbine needs the same things in spades.

So with help of my friends we have developed a 9mm buffer that maximizes the decoupling of reciprocating weight to mostly eliminate closing bolt bounce. Reduce bolt velocity by coupling the weight on bolt open and having total weight of 7.5 oz, decoupled weight of 6.2 OZ and length of 4.125” to reduce bolt travel and further limit bolt speed. Still recommend slightly heavier bolt spring. The combination drops the empty’s cases about eight feet out for both heavy and light loads. First iteration I used hard nylon for rear bumper, too hard, so some soft polyurethane ones are on the way.

So lets hear the comments about my bolt buffer operation

 

[Aircooled6racer]

8 hours ago, cking said:

First observation, most carbine length buffers suck. The worst are the solid ones. Then make the gun feel lousy and make gun bounce worse. Most 9mm bolts are fairly heavy dictated by the nature of blow back. But the space available makes them still too light in AR. So everybody puts a heavy buffer in. Problem also that carbine buffer doesn't leave enough room for the buffer to work like the ones in a rifle.
A Rifle buffer is made of light metal, with heavy weights inside that have lots of room to move.

Movement is the key what I call decoupling of reciprocating weight.

When a bolt is closing the weights help with bolt bounce, but they do something else more important. In a 9mm the bolt doesn’t have the floating rotating bolt carrier design to prolong an eat up energy rotating/locking the bolt. It is just two pieces of metal slamming into each other, thus the forward down pitch of 9mm’s which cause dot bounce. Solid buffers make this worse. More weight stopping quickly/abruptly.

So back to the rifle buffer, as the bolt is closing driven by the recoil spring when it finally comes to a stop. The amount of weight that stops is not the total weight of the buffer, bolt/carrier, and spring. The weights inside the buffer are still moving forward and thus do not contribute to momentum that is converted into felt energy. Eventually they will finally stop, and contribute to the total energy but the time delay greatly reduces the felt impact. So they stop bounce by reducing the effective weight and then delivering delayed impacts to counter the bounce. Upon firing the weights are forward and contribute to the total mass of the inertia needed to be overcome to cause bolt rearward movement.

So the 9mm carbine needs the same things in spades.

So with help of my friends we have developed a 9mm buffer that maximizes the decoupling of reciprocating weight to mostly eliminate closing bolt bounce. Reduce bolt velocity by coupling the weight on bolt open and having total weight of 7.5 oz, decoupled weight of 6.2 OZ and length of 4.125” to reduce bolt travel and further limit bolt speed. Still recommend slightly heavier bolt spring. The combination drops the empty’s cases about eight feet out for both heavy and light loads. First iteration I used hard nylon for rear bumper, too hard, so some soft polyurethane ones are on the way.

So lets hear the comments about my bolt buffer operation

 

Hello: Send me one and I will let you know how it works. Thanks, Eric

[Aircooled6racer]

Hello: Did some testing today with different buffers and springs as well as loads. The best setup so far is 124 grain bullets and 7.5oz buffer with 308 spring. 7-10 yard double taps were right on each other. I tried buffers that are 4.3ozs, 5.4ozs and 7.5ozs with 115 and 124 grain loads at 131-134PF. I still would like to try a heavier buffer still and some more lighter springs. I only had a 308 and 223 springs here to test. I still need to load up some 147 grain bullets also but the 124's are feeling pretty racy.  Thanks, Eric

[corny]

Bring this thread back from the dead...

 

I have two PCC 9mm's.  My 16 inch gun has a Spinta bolt with the weight removed and runs a JP silent captured buffer as it came from them.  1 tungsten and 3 stainless weights.

It has a very light recoil, about half of most other "stock" 9mm AR platform  PCC's.  The recoil is based on t\wo loads.  124 gr Montana gold FMJ HP in front of 4.5 Gr CFE pistol loaded to 1.080 COAL & 147 gr X-Treme FMJ heavy plated bullets in front of 4.2 Gr of CFE pistol, 1.103 COAL.  The 147 grain load and the 124 gr load are nearly identical.  The 147 is a tad softer in my PCC and CZ shadow.  

My "other" PCC has an 8" barrel, CMMG full weight 9mm bolt.  5.5 ounce buffer and a Sprinco .308 extra power spring.  Both of the loads I shoot are the same as above.  The buffer spring setup reduced the recoil about a third from the stock AR spring.  Pulling the charge handle from a closed bolt is "staunch".  Some tuning is in order as I plan on adding a suppressor.  

Edited February 2, 2017 by corny

[ChuckS]

39 minutes ago, corny said:

Bring this thread back from the dead...

 

I have two PCC 9mm's.  My 16 inch gun has a Spinta bolt with the weight removed and runs a JP silent captured buffer as it came from them.  1 tungsten and 3 stainless weights.

It has a very light recoil, about half of most other "stock" 9mm AR platform  PCC's.  The recoil is based on t\wo loads.  124 gr Montana gold FMJ HP in front of 4.5 Gr CFE pistol loaded to 1.080 COAL & 147 gr X-Treme FMJ heavy plated bullets in front of 4.2 Gr of CFE pistol, 1.103 COAL.  The 147 grain load and the 124 gr load are nearly identical.  The 147 is a tad softer in my PCC and CZ shadow.  

My "other" PCC has an 8" barrel, CMMG full weight 9mm bolt.  5.5 ounce buffer and a Sprinco .308 extra power spring.  Both of the loads I shoot are the same as above.  The buffer spring setup reduced the recoil about a third from the stock AR spring.  Pulling the charge handle from a closed bolt is "staunch".  Some tuning is in order as I plan on adding a suppressor.  

Which is faster on the clock?

[Aircooled6racer]

Hello: The stock JP 9mm silent buffer comes with 3 tungsten weights and 1 steel weight with a 308-15 1/2lb buffer spring. It can be tuned to be better. Thanks, Eric

[corny]

9 hours ago, Aircooled6racer said:

Hello: The stock JP 9mm silent buffer comes with 3 tungsten weights and 1 steel weight with a 308-15 1/2lb buffer spring. It can be tuned to be better. Thanks, Eric

Oops, thats what I get for posting before I finish my first coffee.....

 

[corny]

10 hours ago, ChuckS said:

Which is faster on the clock?

The 16" is much faster.  I think it may be due to the extra weight from the 16" barrel. 

I am still tuning the shortie.