Jump to content


Photo
- - - - -

Springs For The 1927


  • Please log in to reply
23 replies to this topic

#1 deerslayer

deerslayer

    Respected Member

  • Board Benefactor
  • 1722 posts
  • Location:North Iowa

Posted 31 October 2004 - 06:13 PM

Finally decided to look into the spring issue on the 1927's. I posted some thoughts and questions here a couple years ago and then Dave J. took up the idea (but hasn't sold us any springs yet), so I went on line, found a spring company and ordered up some of their wares last week. I had a little chance to test things today and so am posting the results.

user posted image

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.
  • 0

#2 Grey Crow

Grey Crow

    RKI Member

  • Board Donor
  • 1077 posts
  • Location:North Central Pennsylvania
  • Interests:Thompson Submachine guns, computers, reptiles.

Posted 31 October 2004 - 09:19 PM

Thanks for the report Dan.

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.

  • 0

#3 PK.

PK.

    Technical Expert

  • Board Benefactor
  • 1567 posts
  • Gender:Male
  • Location:CO, USA
  • Interests:Full time gunsmith who loves Thompsons, 35+ years experience.

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.


  • 0

#4 deerslayer

deerslayer

    Respected Member

  • Board Benefactor
  • 1722 posts
  • Location:North Iowa

Posted 01 November 2004 - 08:59 AM

Good point PK, actually I was thinking of lightening the load, seeing what kind of reduced handload would cycle the bolt. Lot of work I guess, but it will make the gun more pleasant to shoot overall.
  • 0

#5 PK.

PK.

    Technical Expert

  • Board Benefactor
  • 1567 posts
  • Gender:Male
  • Location:CO, USA
  • Interests:Full time gunsmith who loves Thompsons, 35+ years experience.

Posted 01 November 2004 - 10:02 AM

Ammunition with lighter bullets and reduced loads would be an appropriate strategy to reduce the bolt velocity to levels that would be safe with a light spring set, but caution should be exercised to insure the gun is never fired with full power ammunition while the light spring set is installed.
  • 0

#6 giantpanda4

giantpanda4

    Respected Member

  • Board Benefactor
  • 2107 posts
  • Gender:Male
  • Location:Howell, MI 48855
  • Interests:Mechanical toys - cars, instruments, and of course - guns. The 1921-28 thompsons are the epitomy of perfection for a mechanical device that fills all my interests!

Posted 01 November 2004 - 12:43 PM

Dan,

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?
  • 0

#7 deerslayer

deerslayer

    Respected Member

  • Board Benefactor
  • 1722 posts
  • Location:North Iowa

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.
  • 0

#8 LIONHART

LIONHART

    Long Time RKI Member

  • Regular Group
  • 2785 posts
  • Gender:Male
  • Interests:Thompsons of course. All Manufactures and Models.

Posted 01 November 2004 - 04:59 PM

Here's my .02. Congrats on attempting to better the Bolt Assembly for the '27A1 Guns Dan. I would think a Buffer would aid in a better functioning piece, but again, I'm no expert. There is another possible route to take, but it's a little more extreme, which is constructing a new Bolt Assy based around the Semi-Auto UZI Bolt. BTW, FABULOUS Colt 1921 Stock that I received from you. Absolutely perfect. BRAVO my friend!
  • 0

#9 brian

brian

    Regular Member

  • Regular Group
  • 345 posts
  • Gender:Male
  • Location:lebanon,Pa

Posted 01 November 2004 - 07:24 PM

what is the thinking behind the reason to lighten the spring pressure?

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.
  • 0

#10 96lt1ss

96lt1ss

    Regular Member

  • Regular Group
  • 120 posts
  • Gender:Male
  • Location:Home of the St Valentines Day Masacre

Posted 01 November 2004 - 10:36 PM

With all the resources we have there has to be some combination that will effectively reduce the cocking effort without consequences. I think most would agree it's at the top of the list in annoyance in the semi automatics.
  • 0

#11 TommyGunner

TommyGunner

    Long Time RKI Member

  • Regular Group
  • 410 posts
  • Gender:Male
  • Location:Olivebridge, NY
  • Interests:The Tommy Gun (duh)
    Fedora Linux
    Hunting

Posted 02 November 2004 - 07:15 AM


Dan,

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. biggrin.gif

Please keep us posted on how you make out.

Damon

  • 0

#12 deerslayer

deerslayer

    Respected Member

  • Board Benefactor
  • 1722 posts
  • Location:North Iowa

Posted 02 November 2004 - 08:29 AM

I have no plans at all to market a "kit", but I did pass along where I bought the springs, so if anybody has the hots for these things help yourself. Caveat Emptour or something like that.

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...
  • 0

#13 TommyGunner

TommyGunner

    Long Time RKI Member

  • Regular Group
  • 410 posts
  • Gender:Male
  • Location:Olivebridge, NY
  • Interests:The Tommy Gun (duh)
    Fedora Linux
    Hunting

Posted 02 November 2004 - 09:22 AM

Good enough! biggrin.gif
  • 0

#14 Sgt

Sgt

    Long Time RKI Member

  • Board Benefactor
  • 2047 posts
  • Gender:Male
  • Location:Eastern TN
  • Interests:Militaria, Chess, Tools, Sherlock Holmes, Printmaking, UFOs, Ghosts, Electronics, Comic Books, Long walks in the rain, with my Savage 1928a1. (just kidding on the last one; it doesn't have to be raining) -- Ralph

Posted 02 November 2004 - 11:35 AM

Could the 27 bolt be designed to contain a heavier metal, like lead? Maybe that would buffer the action for the weaker springs.
  • 0

#15 deerslayer

deerslayer

    Respected Member

  • Board Benefactor
  • 1722 posts
  • Location:North Iowa

Posted 02 November 2004 - 04:21 PM

Thats another thought I had, drill a few holes in the bolt and pour in some hot lead. The bolt it already pretty hollow though.
  • 0

#16 Sgt

Sgt

    Long Time RKI Member

  • Board Benefactor
  • 2047 posts
  • Gender:Male
  • Location:Eastern TN
  • Interests:Militaria, Chess, Tools, Sherlock Holmes, Printmaking, UFOs, Ghosts, Electronics, Comic Books, Long walks in the rain, with my Savage 1928a1. (just kidding on the last one; it doesn't have to be raining) -- Ralph

Posted 02 November 2004 - 08:23 PM

I wonder if anyone has done a study if it is physically possible to add enough lead to match the weight of the full auto bolt?
  • 0

#17 96lt1ss

96lt1ss

    Regular Member

  • Regular Group
  • 120 posts
  • Gender:Male
  • Location:Home of the St Valentines Day Masacre

Posted 04 November 2004 - 09:47 AM

Instead of lead what about using a different metal for construction, I found this doing some searching:

QUOTE
In fact, the heaviest known metal is osmium, a hard, brittle, bluish-white element about twice as heavy as lead. It gets its name from osme, the Greek word for smell, likely because osmium stinks in some forms.

Osmium has traditionally been used to make really hard alloys for long-wearing things like pen tips. But researchers have recently discovered that osmium is also stiffer than any other material, including diamonds, and therefore stands up best when squeezed at extremely high pressures. This finding could lead to the development of new superhard materials.

Osmium is a hard metallic element which has the greatest density of all known elements. It is twice as heavy as lead, and has a specific gravity of 22.59. (The specific gravity of lead is 11.35; gold is 19.32; and platinum is 21.45.)

Osmium has an atomic weight of 190.2 and its atomic number is 76.



  • 0

#18 Sgt

Sgt

    Long Time RKI Member

  • Board Benefactor
  • 2047 posts
  • Gender:Male
  • Location:Eastern TN
  • Interests:Militaria, Chess, Tools, Sherlock Holmes, Printmaking, UFOs, Ghosts, Electronics, Comic Books, Long walks in the rain, with my Savage 1928a1. (just kidding on the last one; it doesn't have to be raining) -- Ralph

Posted 04 November 2004 - 06:32 PM

I wonder how scarce that stuff is? PK was joking in one of his emails to me and mentioned that we might pack one with Kryptonite.
  • 0

#19 Ron A

Ron A

    Long Time RKI Member

  • Regular Group
  • 641 posts
  • Gender:Male
  • Location:Helena, Montana
  • Interests:Collector of Thompson guns & items<br>Colt single actions<br>Native American items - pre 1900

Posted 04 November 2004 - 08:26 PM

Its interesting the number of posts we have seen on this subject over the many years. 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. Every year we see "new" owners of 27's and they think they are the first to discover and solve the problem. The design has existed since the 80's.

  • 0

#20 96lt1ss

96lt1ss

    Regular Member

  • Regular Group
  • 120 posts
  • Gender:Male
  • Location:Home of the St Valentines Day Masacre

Posted 04 November 2004 - 10:33 PM

QUOTE
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.
  • 0