6.5-270 WSM wildcat

Wants a different 6.5mm cartridge: making a 6.5-270 WSM wildcat

Q: There are so many 6.5mm cartridges on the market that there’s no reason for the added expense and going to a lot of trouble by working with a wildcat — but who ever accused me of being reasonable?

I bought a reamer for the 6.5-270 WSM from Pacific Tool & Gauge and will re-barrel my Winchester Model 70 .264 Win Mag, which has a washed out leade. 

I’ve got a 24” barrel with 1:8 twist and a set of RCBS loading dies. With nearly 200 new .270 WSM cases, I’m am all set to go.

Can you tell me if there are any problems that might crop up with this wildcat? 

What kind of velocity am I likely to get with the good 142gn Nosler AccuBond LR? 

Any other information about forming this wildcat would be much appreciated.

Alex Wilson

A: Most of the problems you might have encountered with the 6.5-270 WSM have been negated by using a long action. If you had been using the short-action Model 70 chambered in .270 WSM you couldn’t have seated bullets out far enough to gain the full potential of the 6.5-270 WSM.

SAAMI specs for the 6.5 WSM call for an overall length of 2.560 to 2.860 inches (65.0-72.6mm), but in the long magazine of your rifle you can seat bullets out to the increased overall cartridge length of 3.365” (85.5mm). 

I’d also recommend a long throat of at least ⅜” (10mm) which will allow greater powder charge weights.

The ideal powders for this 6.5 WSM are in the order of AR2225 and Reloder 33 (if you can find some).

Simply necking down a .270 WSM case is a straight-forward process, but chamber neck diameter may be a problem. It will probably be .299” (7.59mm) and you will be using a .264” (6.71mm) diameter bullet, so case-neck wall thickness is likely to be a critical factor. 

It should be no more than about 0.15” (3.8mm) to allow .005” (or .0025” per side) for bullet release. If you measure wall thickness and it runs thicker than this, case necks need to be thinned and uniformed.

Reaming neck walls to .014 to .015” results in a loaded-round neck diameter of .292 to 294” (7.42-7.47mm), which allows adequate room for bullet release in the .299” chamber.

It is important to develop a load that produces uniform velocity with a case full of powder. 

The two powders I mentioned earlier — RE 33 and AR2225 — both furnish high-density loadings.

Best of luck with this wildcat.




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Nick Harvey

The late Nick Harvey (1931-2024) was one of the world's most experienced and knowledgeable gun writers, a true legend of the business. He wrote about firearms and hunting for about 70 years, published many books and uncounted articles, and travelled the world to hunt and shoot. His reloading manuals are highly sought after, and his knowledge of the subject was unmatched. He was Sporting Shooter's Technical Editor for almost 50 years. His work lives on here as part of his legacy to us all.