Upper question with a twist

[Automan21]

Hey guys. I have a couple of questions. First of all I got a good deal on a 16" upper with BCG and charging handle. The thing is this, it has a flash hider/muzzle brake whatever you wanna call it.
First question is this,
can I smooth off the threads and make it NY compliant?
Second is that its a 1:7 twist I currently have a 1:9 twist NY compliant barrel. Any drawbacks to going down to the 1:7 ?
I ask because I have an Ares SCR and wanted to just swap out the uppers. If all goes well the stock SCR upper will go on the classifieds. Thanks guys.

 

[dsdmmat]

You can remove the threads, I would just pin a thread protector on it and call it good. The 1-7 will stabilize heavier bullets. You can shoot 75,77 and 80 grain bullets with that twist.

 

[Marine Cpl]

Grinding off the threads would make your barrel look bad. I used these barrel caps from Thordsen Customs.

Barrel Cap (plain) for 1/2-28.. | Thordsen Customs

 

[GUNSICK]

Pin a thread protector on it. If you grind off the threads it will look like shit and you will regret it. You can always sell that barrel and get a non threaded one also.

 

[meketrefe]

I agree. during the previous ban a pinned brake, cap or sleeve was considered permanent and there is nothing in the new BS ban
saying that if you had a pinned sleeve it is less permanent. So don't fiddle with the threads. If you have standard threads
they are 1/2" so already too thin for the caliber so I would not touch the muzzle area or crown.
No drawbacks with the 1:7. The 1:7 is really needed by the tracers.
1:9 will do all 70gr excluding solids and some 75gr too excluding VLDs.
fyi.. a 1:8 will stabilize everything up to 80gr excluding VLDs that are a lot longer. 1:8 is also needed for solids in the 70gr-75gr range that are a lot longer.
remember that stabilization is factor of the length and not grain although grain sometimes tells us something about the size
and shape of the average fb/bt bullet.

 

[Marine Cpl]

Unless you plan on shooting those ultra lite grained varmint bullets in the 40 gr range, a 1x7 twist is better. It'll give you the option of firing the higher grained bullets with more length.

 

[dwa12479]

There's not a "drawback" so to say in going to a 1:7 barrel from 1:9, it just depends on what ammo you're using.

Here's what I use for a twist rate guide for barrels. But it's just that... a guide.. not set in stone.

 

[GUNSICK]

Great chart!

 

[togmaster]

Dig the play on words in the title.

 

[Bushmaster]

The twist is a concern, if your building a Predator rifle?

 

[Bushmaster]

Unless you plan on shooting those ultra lite grained varmint bullets in the 40 gr range, a 1x7 twist is better. It'll give you the option of firing the higher grained bullets with more length.

The faster twist spins the bullet faster at a given muzzle velocity. Heavier bullets in a given caliber tend to be longer and the longer the bullet, the faster it must be spun to stabilize it. Willjr is correct.

 

[Bushmaster]

There's not a "drawback" so to say in going to a 1:7 barrel from 1:9, it just depends on what ammo you're using.

Here's what I use for a twist rate guide for barrels. But it's just that... a guide.. not set in stone.

That chart come with 3D glasses LOL...

 

[Automan21]

Wow very good info, thanks guys.

Great chart!

Chart is cool and easy to follow.

Dig the play on words in the title.

Yeah I surprised myself on that one lol.

The twist is a concern, if your building a Predator rifle?

Just basic, nothing crazy.

 

[meketrefe]

The chart is nice but also a bit arbitrary because it does not mention any bullets and only grains.
The stabilization factor depends on lenght, speed, shape and construcion and not grains.
So barnes bullets for example need a faster twist vs a lead core hp for the same gtain.
We also have the ideal twist for terminal performance vs just stabilization as some manufactures might design the bullet to rely
In some yaw to properly work in the target like helping tumbling for example. It is for these reasons we should study the required bullets and ammo and always follow the bullets manufacture recommendations. The 1:8 twist standard in national match seems lile the perfect compromise between slower rates and the rate necessay to send the best match bullets available. This doest mean 1:7 is not appropriate nor 1:9 cannot send some pretty nicel bullets like the legendary 69gr smk or 75gr spbt. But it will not stabilize a 70gr solid like the tsx. (Longer).
The only consideration with 1:7 is that since is designed to stabilize the long military tracers just be careful with the lightest hipervelocity barmint bullets that with very thin jackets might suffer jacket separation due to the additional torque. Not a frecuent event but it happens specially with budget bullets. These come out screaming at 3600+ fps . Also the 55gr m193 will work great from 1:7 since it doest make any significant differnce from 1:9 and it was originally designed for a slower twist. The only exception is the norinco 55gr fmj that for whatever reason tumbles like crazy making it the most effective regardless of the twist. They are hard to find specially since the chinese moved to the 6mm service round.