AEA HP SS Max 357 Project

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caliusoptimus

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Feb 10, 2024
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The HP SS Max 357 was my first pcp. That snowballed real quick into a bunch more, but still a relatively cheap, fun and powerful option. That said it could be a lot better in a lot of ways. This thread is to share my tweaks, addons and improvements.

The biggest annoyance with this rifle is the right hand bolt in conjunction with the right hand magazine. It's a game of twister to insert and remove the mag due to the fact that you have to hold the full force of the hammer spring back with your right hand, flip the rifle over, then reach over the scope to put the mag in place.

I've had a couple of ideas to make this better. First idea was to make a left hand magazine. Second idea was to make a mechanism to hold the bolt back, and to mill the left side of the reciever for an ambidextrous bolt. I'm going to go with the second idea, since it will also make the gun easier for my lefty wife to enjoy.

Another thing is that, while the short barrel is very tacticool, a long barrel would be pretty cool too. I called around looking for a longer one with no luck... so... I went shopping for a blank. I've got the machine to do the work, first time working on a barrel, but I've done many similar cuts and features in the past so probably no big deal.

The HP SS Max could also use a few little accessories... some have already been made and are getting anodized at the moment. Still have a couple more ideas for accessories that may or may not work out.

Probably going to mill the reciever for the lefty bolt today, will at least get it programmed and ready to run.

20240229_083021.jpg
 
Sharp looking max. If you want to get rid of the folding stock piece Texoma precision pellet has a piece that screws into the chassis and then use buffer tubes. I did my 45 max and m50. Gives the gun a whole new feel imo.They always felt wobbly to me and now they are solid. I don't need a folding stock on either one so it worked out .
 
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bearair said:
Sharp looking max. If you want to get rid of the folding stock piece Texoma precision pellet has a piece that screws into the chassis and then use buffer tubes. I did my 45 max and m50. Gives the gun a whole new feel imo.They always felt wobbly to me and now they are solid. I don't need a folding stock on either one so it worked out .
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Thanks!

I managed to shim the hinge on the folding one to get the slop out. The stock still has some slop of it's own though. Does that adapter make hammer spring adjustment any easier? That would be a good excuse for me to get one.
 
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That was a mod I always thought about doing back when I had my HP Max!!
Just couldn’t help but wonder what kinda power it could produce with a longer barrel after seeing the power it made with a mere 13” one..
Unfortunately I never had the machinery to make it happen.
Looking forward to seeing how yours performs with all that barrel length!
 
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Rvaughn said:
That was a mod I always thought about doing back when I had my HP Max!!
Just couldn’t help but wonder what kinda power it could produce with a longer barrel after seeing the power it made with a mere 13” one..
Unfortunately I never had the machinery to make it happen.
Looking forward to seeing how yours performs with all that barrel length!
Click to expand...
I only had a chance to put a few rounds through it before the sun went down... but about 220 foot pounds with a 108 slug at 4kpsi. Based on the 3 or 4 mags I ran through it accuracy has noticeablely improved as well. I'm very excited to sit down and spend some time tuning!
 
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caliusoptimus said:
I only had a chance to put a few rounds through it before the sun went down... but about 220 foot pounds with a 108 slug at 4kpsi. Based on the 3 or 4 mags I ran through it accuracy has noticeablely improved as well. I'm very excited to sit down and spend some time tuning!
Click to expand...

Man!! You have a serious big game rifle on your hands now.. that’s awesome!
Good work!
That’s a lot for a rifle in that weight class, what does it weigh now?
The most I ever got outa mine with the factory barrel was around 140ft/lbs in the stock configuration..

It’ll likely make more power with some heavier ammo too!
 
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Rvaughn said:
Man!! You have a serious big game rifle on your hands now.. that’s awesome!
Good work!
That’s a lot for a rifle in that weight class, what does it weigh now?
The most I ever got outa mine with the factory barrel was around 140ft/lbs in the stock configuration..

It’ll likely make more power with some heavier ammo too!
Click to expand...
It weighs a whole lot now lol. The barrel alone is 5lbs. It shoots well so far, going to contour the barrel which will bring it down from 5 to 1.7lbs.

I spent some more time with it today and I'm thinking it really needs a regulator. With the hammer and pressure maxed out the first shot is great but the next two dump a ton of air, then the remaining shots are decent. With a reg at 225 I think it will have a good balance of energy, velocity and shot count.
 
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Took er to the range today.

I've learned a bit about how the barrel is performing:

JSB pellets, hades and regular - terrible.

NSA 79gn .356 and .357 - not great
NSA 93gn .356 and .357 - not great
NSA 108gn .356 and .357 - a little better
NSA 125gn .357 - best so far

This is 100yds. The 5 left-most shots are NSA 93gn .357. Group on the right is NSA 125gn .357. Both with a regulator at 250 bar.
20240310_154545.jpg


There were some strong gusts on the range today. Not sure how much that had to do with these groups though.

I'm thinking I need to try some longer/heavier slugs. Gonna order some more NSA 125s and NSA 142s. Any other slugs you guys think would be worth a try? The barrel is spot on .357 btw, so I'll stick with that size.
 
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bearair said:
You might want to remove the barrel and push some slugs through it. Also inspect the leade and crown. You might want to lap it if the bore is tight and of course polish it too.
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What am I inspecting the leade and crown for? I machined them myself, they're clean, smooth and burr free. Crown is 11deg, leade gently tapers into the rifling. Both dead on concentric with the bore. I've got the machining thing down, but I don't have a clue about the minutia of crown angles, chamber dimensions etc. More or less copied the chamber from stock, with a slightly tighter leade.

Grooves are spot on .357, bore at .347. Both slightly bigger on one side which became the chamber end.

I've noticed some differences between the new barrel and the stock one... no idea if they're changing things for better or worse... Stock twist is greater than 1 in 24", this is 1 in 20". Stock rifling is a rounded profile, new barrel has sharp square profile. Stock barrel had a bigger bore. Both grooves mic at .357, stock barrel bore is .3525" and new bore is .347".

As far as polishing... I am hesitant. Reading a bit it seems a polished bore fouls very quickly with copper. Couldn't find a direct answer whether lead does the same... my gut says yes.
 
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bearair said:
Sorry brother I didn't realize you had given the barrel all that love. Awesome looking accessories. Top notch. Do you have the tooling to flute the barrel. That would look very cool and probably lighten it up a little.
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No worries man. I COULD flute the barrel... I'd rather turn it down to a smaller diameter but my lathe isn't right for that. I found a local gunsmith that can do it. Hopefully he can do it to my specs, which would bring the barrels weight to 1.7lbs down from 5lbs.
 
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