.457 Extreme

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mackeral5

mackeral5

Member
Dec 24, 2018
480
323
AL, United States
I recently traded for a .457 Extreme. I've never owned a PCP capable of producing over 500fpe so I didn't know what to expect.

This one is in excellent shape, one of the last ones made prior to manufacturing moving to Texas. It is somewhat unique as it only has a 26.5" barrel. Air reservoir appears to hold somewhere around 290cc or so.

As delivered in my opinion it was waaaayyyy oversprung. 

Here are a few strings starting with a 4500psi fill, as delivered.

302 NSA
877
779
714

254 NSA
933
844
761

166 Hunters Supply (160-162 actual)
1082
955
877

My first impression was WOW. I've never shot an airgun this powerful. It was LOUD and tried to blow the lights off my chronograph with every shot. The valve was staying open way too long.

I had to see what was going on inside. This gun is well designed. Very simple disassembly, -118 o-rings which are readily available. Steel poppet and delrin, etc composite seat. Big heavy hammer with a long throw.

In this design the restriction is not in the usual location of transfer or barrel port. The restriction is in the valve throat.

I convert all of my guns to peek poppets so that was the second order of business. The first priority was to open up the throat a bit. I plan to have 2 different tunes, hopefully s 3 shot 400-450fpe tune and s 5 shot 300ish fpe tune. With this in mind I couldnt get carried away and go too big or it would make my low power tune difficult to control ES....



Here are some numbers after increasing the throat diameter and adding a peek poppet.

302gr NSA
913
870
828

920
871
830
End 3200psi

254gr NSA
961
920
863

977
927
878

166 hunter supply
1123
1072
1033
1002
965
936

Now the shot cycles are short and crisp. It no longer wants to blow the lights off my chrony every shot, at least until not the last shot or so of a string, lol.

I have some additional springs on order as well as some 220gr ammo. I hope to be able to find a 3 shot 3800psi tune with the 220gr something like 900-950-900. Then switch to a similar 166gr 5 shot tune simply by changing spring/hammer combinations. I forgot to add I have a spare hammer which I plan to experiment with lighter weights.

I really like this gun, but would have been very disappointed with its tune had I paid retail and then waited for 18 months after ordering for it to be delivered. 

Design and quality are top notch. I am very impressed with the simplicity and ease of disassembly. Being able to change springs and hammers by simply removing the action from the stock and then removing one cap screw holding the end cap in place is genius. 

I think I'll be keeping this one a while.
 
I did some experiments with the a spring and valve opening sequence recently that showed that new dynamic o-rings, Krytox GPL205 grease and a new slightly longer spring tightened up extreme spread on an unregulated PCP. However this was on a balanced valve system. (The old o-rings were creating stiction.) I did one test at a time to verify results.

Your's, in essence, just by just opening up the throat diameter, narrowed the extreme spread by roughly 40 fps across the board. (Did changing the poppet change the weight too?) It would seem that the airflow there (lack of extra air blowing out at the shot) is being somewhat regulated by that bigger hole closing the new poppet quicker (plenum volume and pressure pushing on the poppet). Because this "experiment" in throat size is actually tightening the ES, wouldn't it be wise to continue to open it up a few thousandth at a time and watch the spread shrink, (and speed increasing as well) without changing any other variables first, like hammer weight? Then, once ES it has tightened up more, then add or subtract weight from the equation? It would seem that getting it within 20fps or closer could be had with air and valve volume alone, then work on spring tension to make up the difference at the lower pressure, keeping the whole string tight.
 
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I appreciate the challenging thought processes, i need to give some consideration to them. I don't have much unregulated PCP experience, and even less 500fpe unregulated PCP experience to draw from here. There are 2 factors that I believe are telling me to be conservative on porting. I haven't demonstrated it yet, but I do want to achieve somewhat of a bell curve vs. a downward string. This will come once a few more spring combinations arrive next week.... Secondly, I want to do this with 2 distinctly different tunes, different power levels.

Being this is a traditional, knock-open valve the tuning process is much different than a balanced valve. For example, I have a balanced valve in my unregulated QB .257. With bore-sized porting, it performs much like a regulated gun. with just a 155cc tube, it will produce 5 shots of 100fpe, within 15-20fps of each other before falling off a cliff. This took quite some time to achieve the right balance between hammer weight, balance chamber/throat size ratio, and hammer spring tension. I have not previously experienced a traditional knock-open valve perform like this in an unregulated application, with bore sized porting.

Past experience (albeit a relatively small amount) has shown me that it is a delicate dance of letting the balance between port size, pressure, and hammer strike "self regulate." in this particular gun there will be no easy method of reducing port size, so I'm being very conservative in going larger. 

It is very tempting to step up to a .4125 throat. There is an abundance of hammer strike, so that isn't a concern. I bet it will make over 600fpe. However I think my second tune with higher shot count (5+) 300fpe tune and acceptable ES, will be elusive....likely impossible to find.

I have considered a method of adapting a balance valve to the system, but that may require more precision than my crude tooling is capable of....at least for now.
 
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I've burned up a good bit of lead and nitrogen testing and tuning. So far I've got a couple of decent, repeatable tunes.

A couple of times along the way I attempted to shoot some targets. Each time after a few shots the gun showed that it simply was not going to group decently at 75 yards--5-6 inch groups, I mean patterns. I previously wrote it off to a dirty barrel that would get a thorough cleaning and lapping once the tuning process neared its end.

Well the tuning process is nearing the end so I cleaned and lapped the barrel. Upon slugging I found slugs with smeared engraving....

Close inspection of muzzle revealed this:

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Everything happens for a reason. every cloud has a silver lining, insert whatever your favorite cliche is here.... This prompted me to cross a bridge that I've needed to cross but never had the proper motivation----seek out a local gunsmith....

Low and behold, I found one, 10 minutes from home. Same day service on a cut and recrown job. I will definitely be using their services for future needs!

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I only lost approximately 3/8" of barrel...

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After slugging the barrel again, I'm still getting smeared engraving. It is difficult to see the lead on this gun as the barrel/breech are one unit. But upon close inspection with a light the lead appears to be in as bad if not worse shape than the muzzle. Slugging the barrel still shows nasty smearing on one side of the slug. I pushed an NSA 302gr a few inches into the barrel and then pushed it back out and the same smearing exists, so it appears the problem is at the lead. 

Here are 2 pics taken 180 degrees of each other, a 302gr NSA I pushed through.

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Multiple slugs show the same pattern.

I've ordered a borescope from Amazon, should be able to post pics of the lead later in the week.

Initially when finding the damaged muzzle, I felt odds were this likely happened in manufacturing, but it was possible someone else did the damage. So it was really hard to say what happened. After finding the damaged lead, I am all but certain this occured when the gun was manufactured in Michigan and the Michigan manufacturer knowingly let this mess out of the shop and into the customers hands.....what did they have to lose?? manufacturing was moving to TX anyway.....

More to come once the borescope arrives....
 
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It is definitely tight on that one side of the slug. The bore scope will tell the tale if it is bad machining or lead buildup. Take some pictures with that bore scope setup of the issue so we can all see, as that is a lot of smearing and deformation on that slug!
Click to expand...

Definitely not lead buildup......a thorough cleaning/lapping preceded this slugging. I can see the bad machining but I am not yet equipped to take pics......It looks pretty bad, too..... whatever tooling was used to cut the lead/chamber appears to have been dull and way off center, almost as if the 2 operations were completed on different centerlines....



I've cut a few chambers and leads in a single operation using a modified taper pin reamer and a cordless drill, they are much better than this one. They are also capable of shooting consistent sub MOA groups at 100 yards....


 
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I worked.at Er Shaw barrels for awhile. They are one of our country's biggest barrel manufacturer. Sounds like a shifty factory barrel. All barrels look fancy on the outside but most cheaper barrels are made with world war one machinery that's been in production ever since. Match grade barrel s from.your better manufacturer are probably the way to go if accuracy doesn't improve. Krieger benchmark 

match grade factory lapped barrels. Doesn't matter what u have if the bore is rough it just kinda sucks. Since air guns will never wear out a.barrel I'd buy a.good one. My 2 cents. 
 
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