Proof PXT testing with Alex Wheeler

HellsCanyon said:

When I get my tooling finished for our 7mm's we're going to do a head to head comparison between the PXT and our HC1 rifling.

Mike @ HCA

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Rhovee said:

/300 wsm

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Alex Wheeler said:

I will throw this out there since this barrel tech is the hot topic. I experimented with groove diameters. Most barrels will be made to minimum saami spec plus .0002-.0003". Bore diameters do not effect pressure very much as they are usually 30% of the bore. I had barrels made to a full .001" over saami minimum. Huge velocity increase. If velocity is your main goal, It can easily be done with groove diameters. I wouldnt recommend a full .001" but .0005" was worth over 100 fps in a 6BRA with no negatives. I would not expect better accuracy out of any of this stuff. The design of the rifling is a very small part of what makes a barrel accurate. No matter what accuracy claims are made, I can show you a conventional 4 groove thats done better. Not to say it will be worse, but dont expect better because of the rifling design. I am trying to understand what the main goals are here. Extended barrel life has been mentioned. So long as theres no down side I like that. But Im sceptical, also open minded. Extra velocity, Laying the pressure curve down will allow more powder to be added if the case has the room , if not you went backwards. Going to a faster powder is probably a step back. We'll see how it all plays out. I do expect to see some powder development if this high pressure trend continues. When I was in contact with an engineer for one of the powder manufactures he explained to me they had issues with consistency at extreme pressures. One of the reasons when you get to a point your at real pressure groups get erratic. No longer a stringing that you can fix.

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HellsCanyon said:

Been following along on the PXT thing for awhile. Ironically I have been working on our own patent pending rifling for 6+ months. Conceptualized 2.5 years ago when we started making barrels in house. Finally figured out how to make it beginning of 2026. You'll see something dropping in the next month so I won't share too much here. But it's gonna be big. Solves a lot of the traditional problems with extreme gain twist. This post is the first public mention of it.

I bought a PXT 7mm blank to inspect as soon as they came available. Couple things I found upon initial inspection and casting a lap in it.

1. Pulling a lap through the barrel IS possible, but it is not easy. Not unexpected, nor do I think it's a bad thing. You're helix angle is changing, the bullet engraving is changing, it will have some required effort to pull a lap through.

2. They've got a heavily canted land design, for an "extreme" gain twist it's how I would do it. They put some thought into it. The top of the lands is also very narrow, much much less than the "standard" 2:1 groove to land ratio that you read about. Also not a bad thing, but it is worth mentioning.

3. The barrel pin gauges the same at both muzzle and tennon. Earlier poster claiming the rifling is shallower or not as tall at one end compared to the other is not accurate, at least not on the land height. Both pinned out perfectly at .2770" (saami minimum). I didn't measure the groove diameter but did cast a lap on both tennon and muzzle and the effort to pull the lap through both directions was the same. This tells me they're groove diameters are not tapered. If you have more than about .0002" groove diameter change you definitely feel it in the lap. 5 groove barrels are notoriously hard to measure without a specific ground airgauge probe meant for that rifling profile. I do not have one.

4. The lap when pulled through has the distinct "X" engraving on the "bearing surface" due to the change in twist rate. Expected.

When I get my tooling finished for our 7mm's we're going to do a head to head comparison between the PXT and our HC1 rifling.

Mike @ HCA

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HellsCanyon said:

99% agreed Alex. What I've seen on our HC1 is a maintained accuracy at the pressures where traditional rifling accuracy goes to crap.

Another thing to note is groove diameter gains are very bullet dependent. Some of hornady bullets tend to measure a couple of tenths over nominal, and they absolutely shoot faster with a .0005-.0008" bigger groove. If you're shooting bergers which typically are nominal, it's not much of a factor.

I've also seen tikka barrels that were .001" bigger that were slower than ****....

I haven't measured or confirmed it, but I've suspected that with traditional lead core/copper jacketed bullets that you get some bullet displacement when it's fully engraved thus taking up some of that extra groove diameter that may be bigger than the actual bearing surface OD of the bullet.

Mike @ HCA

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HellsCanyon said:

Been following along on the PXT thing for awhile. Ironically I have been working on our own patent pending rifling for 6+ months. Conceptualized 2.5 years ago when we started making barrels in house. Finally figured out how to make it beginning of 2026. You'll see something dropping in the next month so I won't share too much here. But it's gonna be big. Solves a lot of the traditional problems with extreme gain twist. This post is the first public mention of it.

I bought a PXT 7mm blank to inspect as soon as they came available. Couple things I found upon initial inspection and casting a lap in it.

1. Pulling a lap through the barrel IS possible, but it is not easy. Not unexpected, nor do I think it's a bad thing. You're helix angle is changing, the bullet engraving is changing, it will have some required effort to pull a lap through.

2. They've got a heavily canted land design, for an "extreme" gain twist it's how I would do it. They put some thought into it. The top of the lands is also very narrow, much much less than the "standard" 2:1 groove to land ratio that you read about. Also not a bad thing, but it is worth mentioning.

3. The barrel pin gauges the same at both muzzle and tennon. Earlier poster claiming the rifling is shallower or not as tall at one end compared to the other is not accurate, at least not on the land height. Both pinned out perfectly at .2770" (saami minimum). I didn't measure the groove diameter but did cast a lap on both tennon and muzzle and the effort to pull the lap through both directions was the same. This tells me they're groove diameters are not tapered. If you have more than about .0002" groove diameter change you definitely feel it in the lap. 5 groove barrels are notoriously hard to measure without a specific ground airgauge probe meant for that rifling profile. I do not have one.

4. The lap when pulled through has the distinct "X" engraving on the "bearing surface" due to the change in twist rate. Expected.

When I get my tooling finished for our 7mm's we're going to do a head to head comparison between the PXT and our HC1 rifling.

Mike @ HCA

Click to expand...

Alex Wheeler said:

They were slower with the same load or slower when pressured out? I should have been more specific with my post. The bigger groove let me add more powder and get more speed before hitting pressure signs.

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