7mm LRM neck questions

rgmeddn

Active Member
Joined
Oct 28, 2012
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30
Location
Wisconsin
This is addressed to anybody that is either handloading the promising 7mm Long Range Magnum or to somebody that has more expertise than I. I am seriously considering building one of these and am doing my "due diligence."

The information on the 7mm LRM shows a neck OD of .318" which makes the neck wall thickness .017". I saw one poster mention someplace that the process from the parent 375 Ruger would require neck turning, but that is the only mention of neck turning I have seen. It's a pretty long trip from .375" to .284" and that brass has to go someplace.

Don't misunderstand; I'm not trying to avoid neck turning. In fact I was already thinking that .017" was rather thick. I thought .014 - .015 might be better. The reamer that Gunwerks provides creates a neck diameter of .321" and turning the neck to .015 thickness would increase the neck-to-chamber diameter gap from .003" to .007". If the brass that Gunwerks sells already has been turned and is concentric, that's one thing; but if it needs to be turned then I'm wondering how much neck clearance is considered ideal for what basically is a custom rifle?

So, my questions for anybody that has purchased the 7mm LRM brass (or ammo) are: How are the necks? Have they been turned? Are they equal thickness? Have you measured neck diameter before and after firing?

And for anybody with custom rifle experience, what is the sweet spot for neck clearance for a custom gun of this caliber? I know that mass produced guns run fairly large tolerances to accommodate any factory ammo.

If this resized brass needs to have neck turning to a large enough degree to make the .321" chamber too sloppy, I will either obtain a more optimal version of this reamer or go with something else.

If this resized brass has thick but uniform (turned) necks, I'll experiment with leaving the .003" as is and doing a little turning and comparing .004", .005"

Appreciate any guidance.

rg
 
I am just finishing my 7LRM. I bought some brass to measure it up. I found the necks were pretty inconsistent and had a lot of taper. They got thicker the closer you got to the neck. No way I was going to use it un-turned. I turned it to .015 which gave me a 100% clean up on the necks for a .3145 loaded round over the pressure ring. I speced my neck diameter on the reamer at .318. .003 is as tight as I would go and .004-.005 is preferred IMO.
Also Their throat is way too short. You want to keep the pressure ring of the bullet in the sized part of the neck. To do this with a 180 vld and a 180 hybrid spec your free bore at .150 and at least .2845 on the diameter.
 
Very helpful. Thanks!

So you went with a different reamer than the one Gunwerks sells. What did you do about dies? Gauges?
 
I used the reamer from Gunwerks and turned all my brass to a neck thickness of .016. The rifle is shooting 168s and 180s sub 1/2 moa consistently with Retumbo and H1000.
 
I used the reamer from Gunwerks and turned all my brass to a neck thickness of .016. The rifle is shooting 168s and 180s sub 1/2 moa consistently with Retumbo and H1000.

using which bullet? Hybrid or VLD?I ask because that seems to be the key part of the issue. It seems that the throat of the standard reamer they supply is meant for the VLD but not hybrids. I may be wrong, but that is my understanding.
 
RGMeddn
So far I have used both the vld target and hunter in 168 and the 180 Hybrid....all bullets were seated to within .005 of lands........accuracy has been consistent sub 1/2 moa and no excessive pressure within the loads I have listed.
 
RGMeddn
So far I have used both the vld target and hunter in 168 and the 180 Hybrid....all bullets were seated to within .005 of lands........accuracy has been consistent sub 1/2 moa and no excessive pressure within the loads I have listed.

Can you share your load and velocities with the two different 180s please?
Thanks
 
Can you share your load and velocities with the two different 180s please?
Thanks

7LRM
Gunwerks brass (4th loading) neck sized
Fed 210M primer
180gr. Berger Hybrid P/n 28407
COAL 3.451 (base to ogive 2.723) .005 off lands

71.5 gr Retumbo
Av. vel. 3125 fps
SD 9.0
ES 26


72.0 gr Retumbo
Av. vel. 3148 fps
SD 36
ES 133
 
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