Lightening the BCG

[Blizanthimum]

Has anyone played around with making their BCG lighter, specifically the slug attached to the BCG as pictured ? 

[carharttfarmer]

Easier  to lighten the buffer 

[Jadeslade]

Why would you lighten the BCG in a blowback gun? It doesn't operate like an AR. It just looks like an AR. Not sure why you would lighten a buffer. You may want to tune the recoil spring. by trial and error.

[Blizanthimum]

2 hours ago, Jadeslade said:

Why would you lighten the BCG in a blowback gun? It doesn't operate like an AR. It just looks like an AR. Not sure why you would lighten a buffer. You may want to tune the recoil spring. by trial and error.

Less mass=less optics bounce but more felt recoil.

I have switched from a 5.4oz buffer to a 2.6oz and saw a dramatic reduction in dot movement. I will eventually try a 1oz buffer.

While looking at my bolt the other day, I saw the solid mass pinned to my BCG and thought "why does it have to be so heavy and would lightening it give any benefits?"

[Patrick Scott]

50 minutes ago, Blizanthimum said:

Less mass=less optics bounce but more felt recoil.

I have switched from a 5.4oz buffer to a 2.6oz and saw a dramatic reduction in dot movement. I will eventually try a 1oz buffer.

While looking at my bolt the other day, I saw the solid mass pinned to my BCG and thought "why does it have to be so heavy and would lightening it give any benefits?"

It has to be so heavy to keep the system closed until bore/chamber pressure dissipates to the point where extraction is safe.  If the system opens too soon it will blow out cases. 

[Blizanthimum]

3 minutes ago, Patrick Scott said:

It has to be so heavy to keep the system closed until bore/chamber pressure dissipates to the point where extraction is safe.  If the system opens too soon it will blow out cases. 

Buffer spring tension keeps the bolt closed, not the mass of the bolt.

[Patrick Scott]

6 minutes ago, Blizanthimum said:

Buffer spring tension keeps the bolt closed, not the mass of the bolt.

Physics 101. The heavier the mass the harder is is to get it moving and stop it. By definition mass is the the property of matter that measures resistance to acceleration. 

 

Edited November 10, 2016 by Patrick Scott

[Jadeslade]

19 hours ago, Blizanthimum said:

Less mass=less optics bounce but more felt recoil.

I have switched from a 5.4oz buffer to a 2.6oz and saw a dramatic reduction in dot movement. I will eventually try a 1oz buffer.

While looking at my bolt the other day, I saw the solid mass pinned to my BCG and thought "why does it have to be so heavy and would lightening it give any benefits?"

The buffer makes your dot bounce? Dramatic reduction in dot movement? Where do you shoot? I want to try this. Not believable without actual data. I have an SBR Bushmaster 9mm Carbine. The powder charge controls recoil. I have no trouble hitting the A zone upper or lower at 25 yds. Two shots, fast.

 

19 hours ago, Blizanthimum said:

Buffer spring tension keeps the bolt closed, not the mass of the bolt.

If you think that a spring will keep a bolt closed under the pressures generated in a 9mm blowback gun, guess again. You need to take physics again. A spring, no matter how strong, will not keep the bolt closed without the mass of the bolt being adequate. This is really old science. This is not a lock up system. The weight, sometimes translated as inertia, of the bolt keeps the chamber closed until sufficient pressure is reached. If the bolt opens too early, and the case head blows off, you will lose an eye and maybe more, whatever kind of goggles you wear. This is one of the reasons machine gun design hasn't changed much over the years and licenses to manufacture machine guns are so are so difficult to obtain. There are many companies and individuals with actual miles on this subject. I don't want anyone who reads this to think there is any benefit or that it is safe  to do what you are suggesting. Do what you please to yourself. But don't lead others to think that it is safe or correct or beneficial.  9mm Carbines are not AR type weapons, they are blowback guns. Different design, different operation. 

[Patrick Scott]

29 minutes ago, Jadeslade said:

The buffer makes your dot bounce? Dramatic reduction in dot movement? Where do you shoot? I want to try this. Not believable without actual data. I have an SBR Bushmaster 9mm Carbine. The powder charge controls recoil. I have no trouble hitting the A zone upper or lower at 25 yds. Two shots, fast.

 

 

Jade, I gotta say. Using one given load(130pf), I have also seen differences in dot movement by changing up buffer weights.  I see more dot "pull off" with the system bottoms out in the tube and more muzzle dip when it closes with the heaviest buffer I have on hand(7oz)  The energy built up through momentum of the bolt and buffer has to go somewhere when the system bottoms out and closes up. While I am not a fan of going super light for safety reasons, but I think the conventional wisdom of going heavy in these guns is wrong for our application.  

[dcloudy777]

Reducing BCG/buffer mass and stiffening springs is gonna beat the heck out of a blowback gun,  even if you aren't getting premature bolt opening and blown out cases.

[Patrick Scott]

1 hour ago, dcloudy777 said:

Reducing BCG/buffer mass and stiffening springs is gonna beat the heck out of a blowback gun,  even if you aren't getting premature bolt opening and blown out cases.

You have to remember the original 9mm AR from Colt was designed as a SMG for full power(and hotter) ammo with a buffer weight of 5.5oz and a bolt weight of around 16oz running a standard carbine spring. For USPSA PCC we are running softer ammo and not shooting sustained full-auto. How much slide weight do we commonly strip from our race handguns and how much do we commonly reduce our recoil spring rates by without issue. Common sense would say that we should be able to strip some weight off of our AR  operating system without parts damage as long as we stick to minor PF loads, just like we do when racing .223/5.56 ARs. Maybe not as drastically as our handguns due to the zero lock-up of the system, but as with anything if we go to far stuff is going to break and people could get hurt. Test and tune at your own risk. 

[HawkMoney]

I have a sub 2000. that has a very stiff spring and heavy bolt. It runs winchester white box just fine but its not even close to running my reloads. seems like the only logical thing to do would be to lighten the bolt and spring until its tuned in...

[Jadeslade]

lol. You want to shoot a sub 2000 9mm in competition. awesome trigger pull. come on in. good luck with it. Stock configuration, though.

It may seem logical to you to lighten the bolt and spring in a blowback gun, but it is not logical if you understand why some of us don't want you doing it. This is old science really from the late 1800's and early 20th century,  and good new science from RRA and Bushmaster (old Bushmaster) who did a lot of work in recent years. You might want to ask Kel-Tec about it. It is not safe to lighten up the bolt. experiment all you want, publish some actual data, make your case, but don't just do it and expect good safe guns to result.  You may not care about yourself, but think about the RO and other shooters nearby. The bolt return(the carrier is the bolt in this case) in a 9mm carbine should be smooth and solid, not snappy, or it will bounce. It does not lock. Read some more or talk to some older gunsmiths or armorers. Last post here. 

[HawkMoney]

Can you suggest a good scope mount? I wanna put a really good 1-6 on it. Also everyone lightens the shit out of the bolts on the bennelli's. Thats basically a blowback shotgun whats the difference?

Edited November 12, 2016 by HawkMoney

[wgj3]

I would go with heaviest 1-6 you can find, maybe even something a little stouter like a Bushnell 1-8.5x; you never when those couple of extra "X's" might help. And a stout mount too, like maybe a Bobro. The extra mass on top of the gun should help keep it from moving around too much.

[Patrick Scott]

Looks like the trolls have showed up. Never mind what the guys putting this stuff through its paces are doing, we'll just troll the PCC guys. 

[wgj3]

No interest in trolling here, but the question about a 1-6 on a PCC seemed pretty silly to me...

 

As far reducing recoil/muzzle-rise/muzzle-dip, I was just in a conversation with a buddy of mine about whether or not comps on PCC's are even worth developing.

And, if they are worth developing, do they need to mitigate recoil, muzzle rise related to ultra-hefty bolt and carrier slamming rearward, or muzzle dip related to same ultra-hefty masses slamming back forward.

I'm fairly certain that there isn't enough gas in most of our rounds to accomplish all these things.

Seems a heavier recoil spring might help with rearward movement/muzzle rise, lighter spring might help with forward movement/muzzle dip.

Lighter bullets with more powder(and resulting gas volume) could work comps better. But heavier bullets at lower velocities seem to "feel" better to many.

 

Here is a question that my physics knowledge couldnt seem to overcome...

One load has a 115gr bullet with a powder charge to generate enough velocity to hit a 145PF.

2nd load has a 147gr bullet with a powder charge to reach same PF.

Obviously, the lighter bullets must travel faster and the heavier bullets slower, but what about the velocity of the bolt/buffer? Dos it travel rearward with the same velocity? Back forward at the same rate?

Can I make(commission) an aluminum comp that would hold up to minor PF ammo on a 16" barrel? Would Al be up to the task for a few thousand rounds?

[HawkMoney]

The 115gr load would have more powder than the 147 gr load to achieve the same PF. I would think that would have a different effect on the bolt/buffer movement.

[bmiller]

13 hours ago, HawkMoney said:

Can you suggest a good scope mount? I wanna put a really good 1-6 on it. Also everyone lightens the shit out of the bolts on the bennelli's. Thats basically a blowback shotgun whats the difference?

A benelli has locking lugs.  It is an inertia drive system. The gun recoils around the bolt, driving the bolt carrier forward rotating and unlocking the bolt.  

 

I am all about trying crazy ideas in the name of science.  If you are going to lighten the system that much, why don't you lash the rifle to a tree and use a long string to pull the trigger.  

Edited November 12, 2016 by bmiller

[HawkMoney]

Thats not a bad idea. 

[MikeRush]

I like the way my gun cycles with a standard carbine 3 oz buffer compared to the 5.4 oz 9mm buffer. This is with 148 PF reloads, with a very fast powder and a relatively heavy hammer spring.

I think I am going to remove the center mass of my CMMG bolt, go to a 3.8 oz A5 buffer, and drop 15 pf. I also am going to a shorter barrel with a long, welded muzzle device so that the barrel depressurizes sooner. 

Winchester white box is pretty nasty in my gun- I wouldn't run factory without the bolt mass in and full weight buffer. Even then I have seen some flame out of the ejection port. 

[Flatland Shooter]

Was looking at the New Frontier website.  They offer a "modular" 9mm bolt that the description  indicates it allows "easy carrier weight changes".

Stock it's 16.7 oz. 

So someone out there thinks the idea to put it on a diet has merit.

[TRUBL]

If you are going to put a 1 ounce buffer in a 9mm AR15, you're gonna have a bad time. STD buffer in 9mm with std carbine std is about as light as you want to go, unless you are shooting uber powderpuff loads. 

Get a tubbs flat wire spring and then go thru the paces.......see how that works for you. I think that you will find a heavy buffer with the tubbs spring will work best.....mmmmmmmaybe trimming to suit (we are talking the std tubbs spring that is for rifle and carbine buffers) as the spring may be a little stiff for carbine.

 

[Blizanthimum]

On 11/14/2016 at 5:50 PM, Flatland Shooter said:

Was looking at the New Frontier website.  They offer a "modular" 9mm bolt that the description  indicates it allows "easy carrier weight changes".

Stock it's 16.7 oz. 

So someone out there thinks the idea to put it on a diet has merit.

I will check them out.

[Blizanthimum]

On 11/14/2016 at 9:59 PM, TRUBL said:

If you are going to put a 1 ounce buffer in a 9mm AR15, you're gonna have a bad time. STD buffer in 9mm with std carbine std is about as light as you want to go, unless you are shooting uber powderpuff loads. 

Get a tubbs flat wire spring and then go thru the paces.......see how that works for you. I think that you will find a heavy buffer with the tubbs spring will work best.....mmmmmmmaybe trimming to suit (we are talking the std tubbs spring that is for rifle and carbine buffers) as the spring may be a little stiff for carbine.

 

I had a flat wire spring with a stock 5.9oz buffer and the red dot was all over the place no matter how hard I held it.

Since dropping to a 2.6oz buffer and a standard 223 spring, the dot barely moves and I think it can get better with less mass.