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Old 11-02-2006, 12:59 AM   #1 (permalink)
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MacMurray problem: Spring Combo! (No velocity)

I have a problem with my MacMurray rifle. I can't get it up to respectable velocity. In fact, it will barely pop the valve, it won't get a ball out the barrel. I know why this is happening, but I don't have a solution.

The length of the hammer travel is EXTREMELY short. Here are the dimensions of the various parts:

Depth of rear cap: 25/32" (just over 3/4")
Spring length: 1 + 19/32"
Depth of hammer: 13/16" (just over 3/4")
Length from rear of gun to valve pin: 1 + 5/8"

The video will articulate this problem for you very vividly. When I pull back the bolt, there is quite a bit of travel before the bolt pin ever catches the hammer. I measured the travel of the hammer from rest to the cocked position, and it's a whopping 3/8"! I've even put 4 small threaded nuts in the rear cap and hammer to make the spring stronger (it's very soft without the extra compression). When using a soft valve spring, the valve would stay open (vent) as soon as it was punctured. However, when I put a stronger valve spring in, I couldn't get the velocity up very high at all (hammer doesn't travel far enough to strike spring hard enough.

How do I fix this problem? The Blue Streak sear seems to catch the hammer too early in the length of the hammer's travel rearward. But the rear cap gets in the way of the hammer travelling rearward anymore than that! Here's a video for reference, and a picture of the current trigger/hammer setup:

Video: http://s72.photobucket.com/albums/i1...duerHammer.flv


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Old 11-02-2006, 01:48 AM   #2 (permalink)
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You may need a double sear trigger from a blue streak not the KP2 type you have. Other than that it will take som time in the hands of a willing person to sort out the problem.
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Old 11-02-2006, 01:55 AM   #3 (permalink)
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Aren't the double seared triggers the version that came with kps?
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Old 11-02-2006, 01:57 AM   #4 (permalink)
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Yes, the 2 sear version is from a KP2, this is the single sear version from a Blue Steak, and it's been modified so that the hammer actually catches (the hammer hits the rear plug, and would never catch on a stock trigger sear).

Therein lies another problem: Would I just need to put really strong springs in for the main and the valve? Or would I need to take a Dremel to the rear of the hammer and to the rear plug in order to allow more travel? I really hope this thing can be fixed, it's going to be a blast to shoot when it's done!
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Old 11-02-2006, 08:26 AM   #5 (permalink)
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By the looks of it, that gun was probably never a shooter, more just an display gun.
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Old 11-02-2006, 01:42 PM   #6 (permalink)
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That is a really short stroke! I wonder if the gun was never meant for a stock??? or a trigger group. It does'nt look like the lower tube is extended like other K type sheridans. Try putting a frame on it and see. Also pull the valve and make sure everything is fitting right.

-Jake
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Old 11-02-2006, 01:54 PM   #7 (permalink)
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Well, Peter (Wharf Rat) said that it shot fine the last time he used it in pistol form, so I assume he's correct and that it's shot paint before. I don't have a Sheridan pistol frame to experiment with, but the fact remains that there is only so much distance for the hammer to travel, and even in pistol format, it had to have SOME sort of rear cap in there. Judging by the fact that 2 holes were drilled in the body to hold the rear cap in, and that I had to drill/tap the rear KP plug for those little black retaining screws, I'd say that the short length of the tube is the way it was designed.

Also, I've pulled the valve several times, and I've changed the springs around in several different combinations. I'm just wondering how to lengthen the hammer travel. How far does the hammer travel in an old-style PGP? It must be more than 3/8"!
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Old 11-02-2006, 02:06 PM   #8 (permalink)
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Well, you have to deduce what is limiting the travel. A Pistol end cap is shorter than a K style rear plug/group. Most people run into problems when retrofitting a pistol sheridan to accept the stock/trigger group. This is due to the relationship between the hammer and sear.

Shortening the hammer wont due anything...the hamer is catching in the front on the sear and that location wont change. The pistol frame will allow more travel with the shorter end cap and the sear location is further back also, thus lengthening the hammer stroke.

The only option I see in your situation would be to shorten the hammer at the rear and possibly regrind the sear to move the catch further back. The only issue with shortening the hammer is you will lose the lip that the bolt pin catches on to cock the hammer. You may just need a new, shorter, custom hammer turned.

-Jake
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Old 11-02-2006, 03:24 PM   #9 (permalink)
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what about modding a KP or BS hammer? You could use one of those, possibly shortened, like a typhoon hammer.
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Old 11-02-2006, 04:15 PM   #10 (permalink)
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Quote:
Originally Posted by Azzy View Post
what about modding a KP or BS hammer? You could use one of those, possibly shortened, like a typhoon hammer.

That seems feasible also. You could chop it right sfter the last "rim". I dont know how much shorter that would make it in comparison with a pistol hammer...

-Jake
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