7mm PRC Distance to the lands for factory ammo and reloads

Reloading equipment, methods, load data, powder and projectile information.

7mm PRC Distance to the lands for factory ammo and reloads

Post by Meglaman » 22 May 2024, 4:07 pm

I made a 7mm PRC 30" #9 Heavy barrel with a 1:7 twist in SAAMI spec from a Tika T3 action.

With a 7mm ogive comparator, I measured the Hornady factory ammo, a 7mm Prc 180 gr match. The factory is 2.496”, and the O.A.L Gauge to lands is 2.598”.
The jump is .1030” It seems very large as I have never seen such a big jump.

My reloads are Berger 7 mm 190 Grain Long Range Hybrid Target Rifle Bullet.
With O.A.L gauge to lands is 2.6185. The bullet touching the neck of the case is only a total of .1805” when the neck of the case is roughly .269”

I may have to get a custom reamer because the Berger 180 and 190 bullets are sleeker than the Hornady bullets. At the jam, the Berger 190 is only secured by the neck of the case, which is only a total of .1805” when the neck of the case is roughly .269”. Has anyone had this issue?

I wanted to start at the jam, then move on to two thousand, and slowly move further out, off the lands after powder testing.

I guess the question is, is that enough case neck holding the 7mm Berger? It will only get worse as the lands start eroding over time.

Through reloading, I want it to be half to a quarter MOA barrel.
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Re: 7mm PRC Distance to the lands for factory ammo and reloa

Post by SCJ429 » 22 May 2024, 8:54 pm

You will have to try it and see, you don’t need as much neck engagement as you think. As long as your bullet is straight, you will be fine and with the bullet jammed into the lands you have plenty supporting the bullet. Do a jump test, jammed then 20 thou off, then 40 thou and so on. I wouldn’t bother going past 100 thou but up to you. Most barrels shoot best jammed, but your barrel might be different. Next time discuss with your gunsmith about what bullet you are using and the fact you want to jam the bullet while maximise case capacity.
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Re: 7mm PRC Distance to the lands for factory ammo and reloa

Post by No1Mk3 » 22 May 2024, 9:57 pm

The man who once shot a 1.3" 5 shot 1000yd group doesn't really care about jump, he looks for accuracy nodes and if that is at .010", or .050" it is what it is.
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Re: 7mm PRC Distance to the lands for factory ammo and reloa

Post by in2anity » 29 May 2024, 2:04 pm

Depends how you are shooting now don't it. Single feed a-la NRAA disciplines; not a problem. Hard and fast, PRS style; you'll probs get setback. Horses for courses. Just seat em deeper i say; and fill the case to the base of the bullet with the appropriate powder. Then go shoot. Accuracy is king.
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Re: 7mm PRC Distance to the lands for factory ammo and reloa

Post by Oldbloke » 29 May 2024, 2:53 pm

Historically 0.02" (0.5mm)off the lands works. It's a starting point.

All 3 of my centerfires are just that. All are doing close to or a tad under MOA.

Jamming was the thing once but that can end in a mag full of powder.

As mentioned though each rifle will vary.
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