Buffer Spring Question?

[markm]

I use this setup and it measured exactly what you said it would in a prior post above

Pretty cool rig, but again.... why not just buy in spec springs and change them out periodically???

[Uncas47]

Pretty cool rig, but again.... why not just buy in spec springs and change them out periodically???

Because humans are meddlesome creatures.

[the AR-15 Junkie]

Pretty cool rig, but again.... why not just buy in spec springs and change them out periodically???

I already owned the gauge for checking Motorcycle valve and clutch springs, so decided to see for myself. And how do you know a spring your buying is in spec?

[Uncas47]

Use a trusted source?

[tangolima]

I never liked terms such as " a 15 pound spring", as it doesn't tell you much, but generally is the load developed at solid height, or the maximum force it can develop. Not very useful. (This would be a 12 pound spring) To confuse things, sometimes the term is used to denote the spring rate, (in which case the action spring would be around 1.5 pounds).

Agreed. The confusion comes from that nobody cares to ask for a precise definition. I tried and got different answers from different people who were supposed to know (spring manufacturers). When pressed, they all ended saying "I'm not sure". Finally I got a good answer from an old timer. The spring's poundage is product of its Hook's constant (lbf/inch) and its natural length. Or it is 100x of the pound force produced for each percent change in length.

The carbine spring in your example

Lo = 10.7", K=1.53 lbf/inch

K*Lo=16.3lbf, or it is a 16 pound spring per this definition.

With that calculation actually becomes even simpler. Again for the same carbine spring, as per the forces given, the install length is 6.8", and the compressed length is 3.2".

1.53*(10.7-6.8)=6 lbf
1.53*(10.7-3.2)=11.5 lbf

Or
16.3*((10.7-6.8)/10.7)=6 lbf
16.3*((10.7-3.2)/10.7)=11.5 lbf

Note that the poundage is independent of the spring's natural length, unlike K, which is handy for calculating shortened spring.

2 coils off 38 coils. The new natural length is

36/38*10.7=10.1"

16.3*(1-6.8/10.1)=5.4 lbf
16.3*(1-3.2/10.1)=11.1 lbf

You can arrive at the same figures with the K method.

The force is weaker, but not really alarming. Actually in a quest to make a "gas assisted straight pull action" I cut the spring of an AR -10 pretty short. No problem, not that anyone should try though.

Does solid height mean compressing spring till it coil binds(cannot be compressed anymore)? According to the old timer who explained spring poundage to me, one should avoid that in use. It could pass the spring's limit and it could take a permanent set. There should be limiter in design that keeps this from happening.

-TL

Sent from my SM-N960U using Tapatalk

[lysander]

Does solid height mean compressing spring till it coil binds(cannot be compressed anymore)? According to the old timer who explained spring poundage to me, one should avoid that in use. It could pass the spring's limit and it could take a permanent set. There should be limiter in design that keeps this from happening.

-TL

Sent from my SM-N960U using Tapatalk

NOTE: When counting coils, only count active coils.

The action spring has closed ends, so the last coil on either end doesn't count - 36 active coils.

Solid height (or solid length) is simply, the number of coils (active and inactive) times the wire diameter, it is as short as the spring can physically be (action spring = 2.74"). If you want your spring to last a long time, you should stay at 130% of the solid length for maximum service defection. For the action spring, this would be 3.56", so its design is a little over-compressed. (Just about all gun recoil and magazine springs are. That's why they have relatively short lives, compared to, say car suspension springs.)

[the AR-15 Junkie]

Use a trusted source?

Trust but Verify? Ronald Reagan

Is Sprinco a trusted source?

[Uncas47]

Trust but Verify? Ronald Reagan

Is Sprinco a trusted source?

Not for me.

[Waylander]

This is starting to remind me of the grip screw spec thread.

[556Cliff]

This is starting to remind me of the grip screw spec thread.

Thanks for the reminder because I've been meaning to ask, has there been any new developments in grip screws lately? I hope not, because I'm pretty settled at this point.