Headspace bushing for 338lm (comparator)

[jonaddis84]

Just wondering if anyone can give me the ID of a bushing that will work for 338lm. I dont think it matters as long as you use the same diameter consistently to compare, but wanted to see what a premade one measures out at.

I just got a bushing for 308 and when I got it I realized how simple it was and I shouldve just turned one out real quick on the lathe, which is what Im going to do for a 338 bushing. I thought maybe they had the angle cut into them or something, but no, just straight with a small chamfer.

 

[MitchAlsup]

Re: Headspace bushing for 338lm (comparator)

One of the reasons to have a bushing is so you can dispense with the concentricity damaging expander ball. Another reason is to change the bushing depending on the neck thickness of the cases (at hand).

The main reason is so you can control the neck tension. Desired neck tension is a function of how the ammo is going to be used and how much stress it has to endure between the reloading station and the final firing position. As a general rule:
you want 0.0005-to-0.001 neck tension in benchrest conditions
you want 0.0015-to-0.002 neck tension in tactical bolt gun conditions
You want 0.0025-to-0.003 neck tension in semi-auto conditions

Neck tension as used above is equal to:
LoadedNeckSize = BulletDiameter + 2*NeckThickness
NeckTension = LoadedNeckSize - SizedNeckSize

So given a choice from above of NeckTension, and a measurement of BulletDiameter and a measurement of NeckThickness; 3rd grade arithmetic will allow you to determine which bushing to buy.

 

[jonaddis84]

Re: Headspace bushing for 338lm (comparator)

Maybe I should clarify.

Im speaking of the bushing that inserts into the Hornady locknload comparator body for setting the bump on your FL sizing die.

 

[Fuzzball]

Re: Headspace bushing for 338lm (comparator)

I have no information for what the dataum line for that caetridge is but you are correct that anything contacting the case shoulder around mid-point will work fine. I originally bought two Hornady bushings for my gage kit and have turned five more with complete satisfaction.

 

[tdow]

Re: Headspace bushing for 338lm (comparator)

Giraud Tool makes a headspace/bullet comparator specifically for the .338 LM. Costs about $35.

 

[ChrisGarrett]

Re: Headspace bushing for 338lm (comparator)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jonaddis84</div><div class="ubbcode-body">Just wondering if anyone can give me the ID of a bushing that will work for 338lm. I dont think it matters as long as you use the same diameter consistently to compare, but wanted to see what a premade one measures out at.

I just got a bushing for 308 and when I got it I realized how simple it was and I shouldve just turned one out real quick on the lathe, which is what Im going to do for a 338 bushing. I thought maybe they had the angle cut into them or something, but no, just straight with a small chamfer. </div></div>

It's marked .420".

Which is close to the center of the shoulder proper.

It measures right at .420"

We just call it the headspace insert, not the bushing. Same with the bullet comparator inserts.


Chris

 

[jonaddis84]

Re: Headspace bushing for 338lm (comparator)

Thanks chris, this should only take about 10 minutes and $0.20 worth of aluminum stock to make one up, beats the $15 or whatever Hornady charges.

 

[jonaddis84]

Re: Headspace bushing for 338lm (comparator)

Thanks for the dimensions guys, they turned out great. I was limited by the closest drill size anyway though. I think I ended up with .323 for the bullet comparator (I was told they measure at .322...close enough), and 27/64 (.421) for the headspace.

Wish I wouldve done this before I ordered the 30cal ones!