Jump on AR15

[TommyD11730]

Just wondering on the guys reloading for ARs... did your hand loads shoot more accurately with less jump? Just wondering a generalization in 20" 1-7 barrels. My friend has one we want to make some 69G SMKS for tommorow. He normally just does COAL, but I want to measure and load per ogive.
Just wondering if it's a rabbit hole worth perusing if these guns in general care/don't care about jump.

Thank you.

 

[TheOfficeT-Rex]

Yes and no. Some bullets (RDF) really liked to be closer for me, but the 69SMK shoots just as good with longer jump in my 18" proof.

The bigger issue, is that at mag length nothing is terribly close to the lands.

 

[1fliride]

You will never get close to lands in a factory barrel. Mag length dictates your oal.
Some mags will allow a little longer oal.

 

[TommyD11730]

Yes and no. Some bullets (RDF) really liked to be closer for me, but the 69SMK shoots just as good with longer jump in my 18" proof.

The bigger issue, is that at mag length nothing is terribly close to the lands.

Have you ever thought about modding the mag to accept the longer rounds?
Have you single shot the rounds to confirm that they are more accurate (single shot because they are too long to fit your mag)

 

[TommyD11730]

You will never get close to lands in a factory barrel. Mag length dictates your oal.
Some mags will allow a little longer oal.

I get that but you do have options. If your broke (like me ) you can mod the mags. If you have the coin, longer mags are available for sale.

 

[TheOfficeT-Rex]

Have you ever thought about modding the mag to accept the longer rounds?
Have you single shot the rounds to confirm that they are more accurate (single shot because they are too long to fit your mag)

No. There's nothing to gain by dremel'ing out 10-20k of metal or plastic. You need more than that to get to jam.
Yes, I have single fed them super long, because nothing else I could do with the 70RDF would get them to shoot worth a damn.

 

[TommyD11730]

Not sure if video linking is allowed..

 

[silentwoods]

Wouldn't it be more prudent to install a really accurate barrel if groups are the end game?

 

[TommyD11730]

Sure
However, he has the rifle and the means to reload. If simply reloading and modding the mag makes a big difference sounds like a win to me.

 

[TheOfficeT-Rex]

Sure
However, he has the rifle and the means to reload. If simply reloading and modding the mag makes a big difference sounds like a win to me.

Do me a favour - go measure the thickness of the metal you propose to cut out.

Then, load and shoot a group at the length you could run in your cut out mag, and tell me they run better than those at regular mag lengths. And then tell me how you're going to account for throat erosion to keep that super awesome jump length you just decided on.

Accept the fact that you're not going to load these to jam, and move on. You'll find the SMK profile very tolerant of mag length jump. Failing that, Berger makes a very nice 77, and hornady a 75, that will stabilize in a 1 in 7 and shoot well at mag length.

 

[TommyD11730]

Do me a favour - go measure the thickness of the metal you propose to cut out.

Then, load and shoot a group at the length you could run in your cut out mag, and tell me they run better than those at regular mag lengths. And then tell me how you're going to account for throat erosion to keep that super awesome jump length you just decided on.

Accept the fact that you're not going to load these to jam, and move on. You'll find the SMK profile very tolerant of mag length jump. Failing that, Berger makes a very nice 77, and hornady a 75, that will stabilize in a 1 in 7 and shoot well at mag length.

Good stuff right there. Had I told you he's looking through 4x glass would your head have blown clean off!
You know just because I will load some long. It will be interesting to me, at least to see how much/if they do shoot better.
He also has a few SMK 77g. So, might as well throw them into the mix as well.

 

[Cheyenne Bodie]

Wouldn't it be more prudent to install a really accurate barrel if groups are the end game?

For any barrel there is a load it will shoot best, that is the end game of load dev.

 

[silentwoods]

For any barrel there is a load it will shoot best, that is the end game of load dev.

Mag length= good load development÷goups.

There are a couple of different ways to do this.
Best group for this barrel, apparently that's your plan.

Or best barrel I can get and load the best ammo for it.
I thought you were after the latter, I was wrong.

 

[Cheyenne Bodie]

Mag length= good load development÷goups.

There are a couple of different ways to do this.
Best group for this barrel, apparently that's your plan.

Or best barrel I can get and load the best ammo for it.
I thought you were after the latter, I was wrong.

I'm not after anything, I'm just listening.

 

[silentwoods]

I'm not after anything, I'm just listening.

I understand.

My Noveske 18" spr bbl really likes a 77smk at mag length.