Springs For The 1927
Posted 31 October 2004 - 06:13 PM
From left to right I have the St4-26 spring, the same spring cut to the length I tested, my original bolt spring, a 12649 spring, the 12649 spring cut to length, and my original hammer spring.
To start, I wanted to get the bolt into the same general specs as an M1A1 which would be 7-15 pounds of spring pressure at the start of pulling back the bolt, and full rearward travel. My 1927 with all three springs went from 5 to 32 pounds as issued. The pair of springs that move the bolt went from 5 - 22 pounds and the hammer spring went from 6-10 pounds on my gun (it's short enough that it doesn't really put any pressure on the bolt until it moves a fraction of an inch, then there is basically 6 pounds of force needed to move it).
What I wanted was a hammer spring as weak as possible (but would still explode a primer) and the paired springs which move the bolt as strong as possible. That I felt would remove as much as possible the friction between the striker and the bolt, and still drive a cartridge out of a magazine.
I bought several springs after talking with an engineer over the phone. It's not perfect, but perhaps some of you might want to experiment while we are waiting for Dave to get his stuff for sale.
I ordered four different of the weakest springs I could get. For the pair of springs at the bottom of the bolt, I ended up with springs that were just to weak, even with every bit of length I could cram in there. So, the solution, use one original 1927 spring, and one of the purchased ones.
For the hammer spring, I cut a purchased spring down to the minimum length where it would provide just a little pressure an the hammer, ended up about the same length as the original 1927 spring.
So, what I got was a bolt that started moving at 5 pounds, and reached 21 pounds at full rearward travel. The hammer spring part of that was 1 to 6 pounds, and the unmatched pair on the bottom of the bolt went from 4 to 15 pounds. While not quite as nice as the M1A1 for pulling back the bolt, it was much better than the original bolt extraction force.
I had time (between pheasant hunts) for a short test. 50 rounds of Wolf out of a drum. I ended up with the hammer spring just a touch on the weak side as three rounds did not fire. The primers were very lightly dented. Otherwise, the bolt fully seated the rounds and the gun worked as I would like. I did forget to oil things up really well before leaving the house, so all the bolt parts were pretty dry. That little bit might make the difference with wolf, and perhaps other ammo might be a little more primer sensative.
I may talk to the engineers at Century again and see if they could provide something just a little different. A guy could possibly cut the original 1927 springs down a little, but then you would be sacrificing some of the resistance to motion that the bolt needs to have. As tested the wolf cases were not expanded any more than original spring expansion.
If anybody wants to try this stuff themselves, I contacted Century Spring Corp 800-237-5225. The small diameter recoil spring I ordered was number ST4-26 and the larger hammer spring was number 12649. The two springs cost about $4-$8 each. I'd like to have added one of PK's recoil buffers to the back of the action, but I just couldn't find the extra one I had on hand when I went to shoot.
Dave, if you are out there reading this, we need you to get your springs on the market.
Posted 31 October 2004 - 09:19 PM
I would definitely feel safer having an additional buffer in the works to absorb a little more shock, seeing that a lesser spring would not have quite the breaking effect on the rearward travel of the bolt.
I've been a little paranoid to play with it due to the cost of welding, or replacing the receiver should the impact be a little too stiff.
Edited by Grey Crow, 01 November 2004 - 10:13 AM.
Posted 01 November 2004 - 08:31 AM
I still maintain you cannot simply lighten the springs of semi guns. Everything you mentioned in your testing involved getting the gun to fire and feed- what consideration have you given the other end of the cycle?
The velocity of semi bolt is to high, even with the factory springs- it’s hard to keep the rear sights on, for crying out loud. Lighten the springs and you are asking for trouble- big time.
The only possible way to use light springs is to mitigate the excess bolt velocity with a good buffer system that will actually absorb and dissipate the excess energy.
You have to consider and work on the whole system, otherwise you will break something. I guess it’s good to know that you can buy a new receiver from Kahr.
Posted 01 November 2004 - 08:59 AM
Posted 01 November 2004 - 10:02 AM
Posted 01 November 2004 - 12:43 PM
I will say right off that I haven't seen the guts of the1927.
I will agree with the light loads - but with a warning exactly as PK said, don't ever let full power loads in it again!
But I do see a potential problem. There are more coils on the "shortened " springs that you have shown, compared to the originals. This could cause a condition of coil bind! where the spring "botoms out" under full compression. The loads shoot up astronomically when this happens, and it is not a good thing!
Did yuo check for coil bind?
Posted 01 November 2004 - 02:12 PM
Another good point.
The springs are smaller diameter wire, and will fully compress on the guide rods without "bottoming out" The is plenty of extra room on the hammer spring. The smaller spring is at the maximum length without having too much spring to bottom out.
Posted 01 November 2004 - 04:59 PM
Posted 01 November 2004 - 07:24 PM
having one of pk's modifies actuators, i do "notice" the effort to get the beast cocked, the first time, however it's not so bad as i think much about it.
as a side note to the rear sights not staying on. mine shot off not long ago, when it did so, it stripped ALL 4 holes in the receiver of their threads. it also bloodied the shooter's right eye.
Posted 01 November 2004 - 10:36 PM
Posted 02 November 2004 - 07:15 AM
I am pleased you took this on. As you may know Merle is in the buffer business and is going to produce a very nice 21/28 buffer. Perhaps he could be of help in getting a buffer together for your application here. If you can get these together...I am in. If I can help you out in any way please let me know. There is one thing that could be a potential issue if you make and sell a kit...liability. If the spring kit should cause a problem that results in injury to a shooter...could be a serious lawsuit...I think that is why Dave J. needed an LLC to produce them. Kahr and Numrich were aware of this and were very carefull in their design and manufacture of the guns...they wouldn't want a rear sight to come off and bust someone in the eye or anything.
Please keep us posted on how you make out.
Posted 02 November 2004 - 08:29 AM
What I would like to do is get a very small roller bearing to put on the pins that hold the striker in place. That I'm sure would also smooth things up. Next project...
Posted 02 November 2004 - 11:35 AM
Posted 02 November 2004 - 04:21 PM
Posted 02 November 2004 - 08:23 PM
Posted 04 November 2004 - 09:47 AM
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Posted 04 November 2004 - 06:32 PM
Posted 04 November 2004 - 08:26 PM
Posted 04 November 2004 - 10:33 PM
|Do you think AO didn't know the problem with the hard to open bolt, and not tried to correct the problem in the original design.|
My honest opinion is they don't care, the gun works and sales are good. From their prospective why bother investing the dollars in R & D along with the cost to retool the production line.