Barrel tension, C.O.A.L., and bullet jump

[svxwilson]

We you swap or reinstall a barrel on a AR can the amount of torque you put on it affect the Amount of bullet jump to the lands?

In the last few months I have got a Hornady bullet comparator Along with a O.A.L. GAUGE. I have been measuring my distance to the lands and found that on my brand new SCAR 17 that it is right where it is meant to be. If I loaded to max mag 2.82" length I would be jamming them (bullets) into the lands. Have not done any reloading for this yet. Just got it fri.

I have a Smith&Wesson M&P10 and a BRO pg15 (both 308's) I have had the same smith do some work that required he reinstall the barrel. If I tried to get anywhere close to the lands on both of those the ammo would not fit into the mag. The bullet sizing is exactly the same for both(found this very odd). Both the M&P and the BRO have had 200-300 rnds down them. They should not be shot out yet. Is this the way they are from the factory (long bullet jump).

Have been paying attention to what people post their 308AR max oal to be. the scar is right in line with all the other guns. But my AR308s have a lot of jump.

 

[sawman556]

I'm not sure how the torque value of the barrel nut would have anything to do with what's going on inside the chamber.

 

[wareagle700]

No. The headspace is set when the barrel extension is installed. The case does not go farther into the chamber with more torque.

Some rifle barrels are just chambered with a longer throat (more jump length). With cheaper rifle's and factory barrels this is more common. With gas guns, the thing to do is load your ammo to 2.800" - 2.820" and shoot bullets that are jump friendly. Don't get caught up in trying to chase the lands, just load to mag length and play with the powder charges to find the accuracy node. You can still get great accuracy with a jump.

 

[svxwilson]

shoot bullets that are jump friendly. You can still get great accuracy with a jump.

What bullets are jump friendly? I just thought it was odd that both AR's had the identical measurement. Only thing they have in common is the same smith worked on both. I don't have the tools to do barrel swaps, I have never seen it apart. Excuse my stupid question. I would like to acquire a vise and torque wrench but my space is limited right now.

 

[wareagle700]

Sierra matchkings, Berger hybrids, any bullet with a tangent ogive.

 

[sawman556]

Not a stupid question. Sorry if I made it sound that way.

I wouldn't mess with the barrels unless you plan on swapping them out for something custom from a skilled smith that knows how to chamber a quality blank and install a barrel extension. It might be best to just live with the jump. What kind of accuracy are you getting from them now?

I'm not saying it's impossible but I never expect the same accuracy from a semi-auto that I do from a custom bolt-action.