Predom Lucznik Model 70

[Steveoo]

Thanks Stevoo. This little beast is pretty interesting as this is my first "springer" of any kind.

What exactly does the screw in front of the trigger do/adjust? Why such a long screw?

It is effectively useless in the normal sense of trigger adjusting.
If you look closely, you will notice a small travel limiting block which this screw shifts slightly but a forward limiter is not something we usually see on a pistol. It does not alter pressures, or stages like other guns.
However, the trigger is not too bad once polished and lubricated …just forget it and dont worry about it.
As a word of warning….do not ….ever …remove the trigger blade from a LP53 or Lucznik.
The replacement of the little trigger group components requires the use of a little slave pin which you will need to make…a real PITA

 

[Roboslug]

Steveoo, thanks for the screw info. Don't worry I won't even consider taking the PL apart any further especially since there is such little info regarding these pistols.

 

[Roboslug]

On another thread regarding an HW70 "Barrel pivot tension adjusted, relubed" was mentioned. The PL has an interesting "lockscrew" the goes into the barrel pivot pin. While locktite can hold it in place, is there a "correct" tension/torque for a barrel tension screw? Thanks.

 

[Steveoo]

Not to my knowledge. The locking screw merely serves to slightly splay the end of the thread of the larger pivot screw to prevent it coming unscrewed. Nothing special required …just nip it up.
The main concern, based on my experience, is to degrease the inner thread of the main pivot screw and degrease the threads of the lock screw so it stays done up….left greasy, it will keep coming loose on you.
You want a faint hint of moly on the smooth dia of the pivot pin but keep it down as it will be squashed into the threads when tightening up…..just a meniscus is all that is required…

Perform every task with the greatest of care, or this gun bite you in the ass, but get it right and it will reward you.
Despite the upward shunt, of this gun and the LP53 its a very singular, repeatable recoil and once mastered can make astonishing accuracy….going much further than the HW45 or Webleys…ive even known them beat FWB 65s in the right hands.

 

[Roboslug]

Thanks Steveoo. I've shot pistols (powder burners & Co2) for over 50 years, but nothing is as intriquing as this PL. It is amazing accurate IF it is held properly. The attached 5-bull target card is my most consistent to date. I have had 5 shot groups that were half this size, but only a couple, not 5 on the same card.

Last week I passed the 1,000 pellet mark with a combination of HN & RWS wadcutters. Some JSB domes should arrive soon. I am not good enough with this pistol yet to declare which one it prefers as it has printed spectacular groups with each. Any of them shoot well if I do my part.

 

[Steveoo]

Good shooting, you will improve…..ive had those groups at 10 and 12 yards.
If possible use a Brass round head screw in a battery drill to dress the muzzle….i also did the breech.
Try Air Arms AA pellets, Geko also good in these…H&N match lights.
Really ramp things up with a red dot…

 

[Roboslug]

Thank Steveoo. The brass screw dressing is a great idea. I have red dots on my other pellet pistols and they help immensely. The iron sights on the PL aren't too bad. My plan is the get consistent groups with the iron sights, then reward myself with a red dot.

 

[Roboslug]

Still working on accuracy with the Predom, but I did purchase a $3x amazon chronograph. The pellet is H&N Sport 4.50, 8.18 gr.

V1	362​
V2	357​
V3	361​
V4	362​
V5	356​
V6	348​
V7	353​
V8	353​
V9	359​
V10	361​
V11	365​
V12	355​
	357.67​	ave velocity
	4.89​	std. dev.

 

[Roboslug]

Sometimes when shooting the PL the spring cap comes slightly loose. When tightening the usual squeaks and groans occur from the springs which means they are being wound up and de-coiled at the same time. So without a cut spring and delrin top hats I made some washers out of .06" polystyrene sheet. Why that material? - it was in the house the time. It does add a slight pre-load to the springs, but there is no noise when the cap is installed or when cocking. The shot cycle is much smoother and velocities are higher.

Pellet	HN Sport	HN Finale Heavy Match	HN Sport	HN Finale Heavy Match
Nominal Dia	4.5​	4.5​	4.5​	4.5​
Nomimal Wt	8.18​	8.18​	8.18​	8.18​
			w/poly washers	w/poly washers
V1	362​	372​	378​	383​
V2	357​	369​	385​	383​
V3	361​	365​	375​	378​
V4	362​	366​	372​	379​
V5	356​	363​	373​	382​
V6	348​	365​	377​	374​
V7	353​	360​	390​	383​
V8	353​	364​	376​	383​
V9	359​	363​	375​	380​
V10	361​	366​	382​	385​
V11	365​	365​	378​	386​
V12	355​	359​	374​	380​
ave velocity	357.67​	364.75​	377.92​	381.33​
std. dev.	4.89​	3.52​	5.30​	3.31​

 

[Steveoo]

The grip cap on both the Predom and the LP53 unwinds due to the rotational thrust of the mainspring as it uncoils.
Offering perfect proof to the doubters of rotational torque being given up to springer airguns.
So much so, that ive known a grip cap to completely unwind across a 100 shot shooting session with an LP53, if gone un-noticed, jettisoning mainsprings out the base of the gun….quite an alarming experince.

I achieved big reductions in this torque by employing Delrin guides/ Top hats, and as a fun trade off, my LP53 proved to be the best test bench ever for anti torque material experiments.
I think maybe its combination of having an end cap which unwinds easily under this torque, offering a sensitive test bed, but also the speed that you can open the gun to make any such changes easily.
Pretty much making me the guru on thrust material experiments.

Results…
One of my shock findings is that of Tinbum and Eagle kits performing quite badly in regard of torque removal if you do not go with the following advice..
Delrin which they employ proved to be fantastic low torque material with medium Carbon steel like mainsprings or steel thrust washers, but employ a thrust washer of the same material as provided in their kits and you cancel out the low friction benefit. 2 like materials acting on each other, pick up on the faces and rub on each other, reducing efficiency below that of plain old mild steel…

I got superb results from employing a delrin guide with a Nylatron thrust ring, slightly bettering a plain guide of Delrin acting directly on the steel mainspring….and zero grip cap unwind.
It suggests that if you use these kits, you should use them without the slip washers, or machining them up out of a different material.

 

[Roboslug]

For the last couple of days my Predom has unlatched, just slightly, when fired. It happens randomly with any pellet. Any ideas would be appreciated.

 

[Steveoo]

The barrel unlatches due to the detent spring being on the edge of things, particularly with the Predom.
This is easily rectified by employing a slightly stronger detent spring…
I cannot help you with the exact specification for the little spring, as years ago I realised the value of purchasing a mini spring selection box….They do not cost much to buy, and usually offer any permutation you can think of for trigger springs and sears etc…
I chose a 4.5mm OD 1 mm wire and snipped the 30 mm length to about 1/2 inch long for the very positive lock up i get on the LP53..

The value of a small spring and O ring selection box cannot be stated enough.

 

[Roboslug]

The barrel unlatches due to the detent spring being on the edge of things, particularly with the Predom.
This is easily rectified by employing a slightly stronger detent spring…
I cannot help you with the exact specification for the little spring, as years ago I realised the value of purchasing a mini spring selection box….They do not cost much to buy, and usually offer any permutation you can think of for trigger springs and sears etc…
I chose a 4.5mm OD 1 mm wire and snipped the 30 mm length to about 1/2 inch long for the very positive lock up i get on the LP53..

The value of a small spring and O ring selection box cannot be stated enough.

Thanks, I wondered about the LP53 as well. Comparing the two, the PL spring looks much smaller. I'll post what I come up with.

 

[Steveoo]

The LP53 lock up strength is about 25 percent better based on the OEM spring strengths.
You can easily get away with a full coil extra or a pair of 4mm O/D spacing washer under the OEM spring.
Detent sear is massively robust on either gun and unlikely to be comprimised by the extra spring power…..mine hasnt anyway across 1000s of rounds..

 

[borne2fly]

I went through much the same process on my Predom.
Shimmed the barrel gap (pivot screw) with precision steel washers to take up the slop. The Diana model 5 already has these, I just copied that.
For a moment I though about boring out the barrel and shoving in a full-length barrel, but that would bugger up a classic pistol

 

[Roboslug]

My PL and I have come to an agreement where I don't take it apart trying to "improve" the latch spring and it stays closed while firing by simply snugging the pivot screw about every 100 shots or so. Hopefully the spring & guide modifications will happen this calendar year.

 

[Modski66]

Not had an issue with the latch on mine so far, but I don't think it has been used very much as it is in excellent condition. My plan is to fit a cut-down HW30 spring with a Delrin sleeve over the existing guide and a Delrin top-hat in the piston, the transfer port is also going to be sleeved down to 3mm.
These are all inspired by @Steveoo and his LP53 modifications; I my swap the top-hat to steel if I am not getting the fps high enough for the pellet to leave the barrel before the recoil kicks in.

 

[Steveoo]

If you cut your Top hat to have a major dia of 18.80 x 3mm for the lip, it will have a nice 0.2mm of clearance inside the piston. The stem part which slips inside the mainspring needs to be 12.70 dia x approx 15 mm length....total length of approx 18mm.
This will give you approx 10 grams if in steel....with the 8mm hole drilled through the middle of it to accomadate the top of the guide as it goes just inside the top hat at fully cocked.
Dependent on quality of the piston chamber, I've had between 485 to 530 fps and zero vibration with this set up....MY honed parallel piston chamber giving 530 fps.

 

[Roboslug]

If you cut your Top hat to have a major dia of 18.80 x 3mm for the lip, it will have a nice 0.2mm of clearance inside the piston. The stem part which slips inside the mainspring needs to be 12.70 dia x approx 15 mm length....total length of approx 18mm.
This will give you approx 10 grams if in steel....with the 8mm hole drilled through the middle of it to accomadate the top of the guide as it goes just inside the top hat at fully cocked.
Dependent on quality of the piston chamber, I've had between 485 to 530 fps and zero vibration with this set up....MY honed parallel piston chamber giving 530 fps.

Steveoo, is a steel top hat more desirable than delrin/nylon/plastic for increased weight?

 

[borne2fly]

How is a Predom breech seal replaced?
I haven’t dared to fiddle with it as it appears to be a very thin layer of something pretty delicate